Catalytic system for olefin oxidation to carbonyl products

ABSTRACT

The present invention provides aqueous catalyst solutions useful for oxidation of olefins to carbonyl products, comprising a palladium catalyst, a polyoxoacid or polyoxoanion oxidant comprising vanadium, and chloride ions. It also provides processes for oxidation of olefins to carbonyl products, comprising contacting olefin with the aqueous catalyst solutions of the present invention. It also provides processes for oxidation of olefins to carbonyl products by dioxygen, comprising contacting olefin with the aqueous catalyst solutions of the present invention, and further comprising contacting dioxygen with the aqueous catalyst solutions. The present invention also provides a process for the oxidation of palladium(0) to palladium(II) comprising contacting the palladium(0) with an aqueous solution comprising chloride ions and a polyoxoacid or polyoxoanion oxidant comprising vanadium.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 489,806 filed Mar. 5, 1990 now abandoned which isincorporated by reference entirely. Related U.S. patent applicationsSer. Nos. 07/689,050, 07/689,048, and 07/675,937, co-filed with thisapplication on Sep. 4, 1992, are each incorporated by referenceentirely.

FIELD OF THE INVENTION

This invention relates generally to oxidation of olefins to carbonylcompounds. More specifically, it relates to oxidation of olefins tocarbonyl compounds by polyoxoanion oxidants in aqueous solution,catalyzed by palladium. In another aspect, it relates to reoxidation ofreduced polyoxoanions in aqueous solution by reaction with dioxygen. Itfurther relates to an overall process for the oxidation of olefins tocarbonyl compounds by dioxygen catalyzed by palladium and polyoxoanionsin aqueous solution.

BACKGROUND OF THE INVENTION

The catalyst solutions and the processes of the present invention areuseful for the production of aldehydes, ketones, and carboxylic acids,which are chemicals of commerce and/or feedstocks for the production ofchemicals and materials of commerce. For example, acetone, methyl ethylketone and methyl isobutyl ketone are used as solvents. Acetaldehyde isused in the production of acetic acid, polyols, and pyridines. Aceticacid is used in the production of vinyl acetate, cellulose acetate, andvarious alkyl acetate esters which are used as solvents. Acetone is usedin the production of methylmethacrylate for polymethylmethacrylate.Cyclohexanone is used in the production of caprolactam for nylon-6 andadipic acid for nylon-6,6. Other cyclic ketones can be used for theproduction of other nylon-type polymers.

Acetaldehyde is industrially produced by the Wacker oxidation ofethylene by dioxygen, which uses an aqueous catalyst system of palladiumchloride, copper chloride, and hydrochloric acid to accomplish thefollowing net conversion:

    C.sub.2 H.sub.4 +1/2O.sub.2 →CH.sub.3 CHO           (1)

Reviews of the Wacker process chemistry and manufacturing processes forthe direct oxidation of ethylene to acetaldehyde can be found in "TheOxidation of Olefins with Palladium Chloride Catalysts", Angew. Chem.internat. Edit., Vol. 1 (1962), pp. 80-88, and in Chapter 8 of Ethyleneand its Industrial Derivatives, S. A. Miller ed., Ernest Benn Ltd.,London, 1969, each of which is incorporated by reference entirely.Aspects of Wacker technology are also disclosed in U.S. Pat. Nos.3,122,586, 3,119,875, and 3,154,586, each incorporated by referenceentirely.

In the Wacker process chemistry, ethylene is oxidized by cupric chloridein aqueous solution, catalyzed by palladium: ##STR1##

In a typical manufacturing operation, copper is present in the aqueoussolution at concentrations of about 1 mole per liter, total chloride ispresent at concentrations of about 2 moles per liter, and the palladiumcatalyst is present at concentrations of about 0.01 moles per liter.Under these conditions, palladium(II) exists predominantly as thetetrachloropalladate ion, PdCl₄ ⁼. Cuprous chloride resulting from theoxidation of ethylene is solubilized in the aqueous solution by theco-produced hydrochloric acid, as the dichlorocuprate ion, Cu^(l) Cl₂ ⁻.In a subsequent Wacker chemistry step, this reduced copper is reoxidizedby reaction with dioxygen:

    2Cu.sup.l Cl.sub.2.sup.- +2H.sup.+ +1/2O.sub.2 →2Cu.sup.ll Cl.sub.2 +H.sub.2 O                                                (3)

(Reactions (2) and (3) combined give overall reaction (1))

Two acetaldehyde manufacturing processes, a two-stage process and aone-stage process, have been developed and operated using the Wackersystem chemistry. In the two-stage process, ethylene oxidation by cupricchloride, reaction (2), and reoxidation of cuprous chloride by air,reaction (3), are conducted separately, with intermediate removal of theacetaldehyde product from the aqueous solution. The reoxidized aqueoussolution is recycled to the ethylene oxidation stage. The reactions areconducted at temperatures of about 100 to 130° C. in reactors which, byproviding very efficient gas-liquid mixing, result in high rates ofdiffusion (mass transfer) of the reacting gas into the aqueous solution.Under these conditions, about 0.24 moles ethylene per liter of solutioncan be reacted within about 1 minute in the ethylene reactor,corresponding to an average ethylene reaction rate of about 4(millimoles/liter)/second. With a typical palladium concentration ofabout 0.01 moles per liter, this corresponds to a palladium turnoverfrequency (a measure of catalyst activity) of about 0.4 (moles C₂ H₄/mole Pd)/second. In the air reactor, about 0.12 moles dioxygen perliter of solution can be reacted within about 1 minute, corresponding toan average dioxygen reaction rate of about 2 (millimoles/liter)/second.

In the one-stage process, ethylene and dioxygen are simultaneouslyreacted with the aqueous solution, from which acetaldehyde iscontinuously removed.

Palladium catalyzes the oxidation of ethylene by cupric chloride(reaction (2)) by oxidizing ethylene (reaction (4)) and then reducingcupric chloride (reaction (5)):

    C.sub.2 H.sub.4 +PdCl.sub.4.sup.= +H.sub.2 O→CH.sub.3 CHO+Pd.sup.0 +2H.sup.+ +4Cl.sup.-                                      ( 4)

    Pd.sup.0 +4Cl.sup.- +2Cu.sup.ll Cl.sub.2 →PdCl.sub.4.sup.= +2Cu.sup.l Cl.sub.2.sup.-                                 ( 5)

Functionally, the copper chlorides mediate the indirect reoxidation ofthe reduced palladium(0) by dioxygen via reaction (5) plus reaction (3).Direct oxidation of palladium(0) by dioxygen is thermodynamicallypossible but is far too slow for practical application.

The overall rate of oxidation of ethylene by the Wacker system islimited by the rate of oxidation of ethylene by the tetrachloropalladate(reaction (4)). The reaction rate is inversely dependent on both thehydrogen ion concentration and the square of the chloride ionconcentration, having the following concentration dependencies:

    C.sub.2 H.sub.4 reaction rate∝[PdCl.sub.4.sup.= ][C.sub.2 H.sub.4 ]/[H.sup.+ ][Cl.sup.- ].sup.2                             ( 6)

Two chloride ions must be dissociated from tetrachloropalladate beforepalladium(ll) productively binds both the substrates of reaction (4),ethylene and water. Said another way, chloride competes with the twosubstrates for the third and fourth coordination sites on palladium(ll).This occurs by the following equilibria:

    PdCl.sub.4.sup.= +C.sub.2 H.sub.4 ⃡PdCl.sub.3 (C.sub.2 H.sub.4).sup.- +Cl.sup.-                                  ( 7)

    PdCl.sub.3 (C.sub.2 H.sub.4).sup.- +H.sub.2 O⃡PdCl.sub.2 (C.sub.2 H.sub.4)(H.sub.2 O)+Cl.sup.-                     ( 8)

Not only does chloride ion competitively inhibit the binding ofsubstrates, but the remaining bound chlorides in intermediate complexesdiminish the electrophilicity (positive charge density) at thepalladium(ll) center which drives the overall reaction to palladium(0).The subsequent reaction steps, hydrogen ion dissociation (reaction (9))and collapse of the resulting intermediate to products (reaction (10)),are less favored for these chloride-bound intermediate complexes thatthey would be for their aquated counterparts with fewer or no boundchlorides.

    PdCl.sub.2 (C.sub.2 H.sub.4)(H.sub.2 O)⃡PdCl.sub.2 (C.sub.2 H.sub.4)(OH).sup.- +H.sup.+                               ( 9)

    PdCl.sub.2 (C.sub.2 H.sub.4)(OH).sup.- →CH.sub.3 CHO+Pd.sup.0 +H.sup.+ +2Cl.sup.-                                       ( 10)

A step in reaction (10) is turnover rate-limiting for reaction (4) inthe Wacker system (reactions (7), (8), (9), and (10) give reaction (4)),so that the disfavoring influences of chloride ion on reaction (10) andon the preceding equilibria (7), (8), and (9) are manifested in theobtained palladium catalyst activity.

However, the Wacker system requires a high total chloride concentrationto function effectively. The chloride to copper ratio must be greaterthan 1:1 for the copper(ll) to be soluble CuCl₂ rather thaninsufficiently soluble copper hydroxide chlorides, and for copper(l) tobe soluble CuCl₂ ⁻ rather than insoluble CuCl. Moreover, in the absenceof chloride, aquated copper(ll) is thermodynamically impotent foroxidizing palladium(0) metal to aquated palladium(ll). Chloridecomplexation raises the copper(ll)/copper(l) oxidation potential andlowers the palladium(ll)/palladium(0) oxidation potential, so that athigh chloride ion concentrations the forward reaction (5) becomesthermodynamically favored.

The Wacker system has several undesirable characteristics in themanufacture of acetaldehyde. These undesirable characteristics resultfrom the high cupric chloride concentration. The aqueous cupric chloridesolution is extremely corrosive; manufacturing process equipment isconstructed of expensive corrosion resistant materials, usuallytitanium. The manufacturing processes typically convert a percent ormore of the ethylene feed to chlorinated organic by-products. Thesechlorinated organic by-products are hygienically and environmentallyobjectionable. Their adequate separation from the acetaldehyde productand from other gas and liquid streams which exit the process and theirproper destruction or disposal add to the operating costs of themanufacturing processes.

These chlorinated organic by-products have a number of mechanisticorigins. Some result from direct additions of hydrochloric acid toethylene, giving ethylchloride, and to olefinic by-products. Othersresult from palladium centered oxychlorination, for example,2-chloroethanol from ethylene. The predominant origin of chlorinatedorganic by-products is oxychlorination by cupric chloride, most arisefrom copper centered oxychlorination of acetaldehyde, givingchloroacetaldehydes, and further reactions of the chloroacetaldehydes.Accordingly, we determined that most of the objectionable chlorinatedorganic by-product yield results not simply from the presence ofchloride, but from the combination of chloride and copper.

Aqueous palladium(II) salts also oxidize higher olefins to carbonylcompounds according to equation (11), where R, R', and R" arehydrocarbyl substituent groups and/or hydrogen (R=R'=R"=H for ethylene):##STR2##

As examples, aqueous palladium(II) salts oxidize propylene to acetone(and some propionaldehyde), butenes to methyl ethyl ketone (and somebutyraldehyde), and cyclohexene to cyclohexanone. Higher olefins can beoxidized by dioxygen using the Wacker system, but serious problemsencountered in using the Wacker system to oxidize higher olefins haveeffectively prohibited any other significant application tomanufacturing carbonyl compounds.

The rate of oxidation of the olefinic double bond by aqueouspalladium(II) salts generally decreases as the number and/or size ofhydrocarbyl substituents increases. This decrease in rate isparticularly severe with PdCl₄ = in the Wacker system, due to thecompetition of chloride with the more weakly binding higher olefins forpalladium(II) complexation and due to the lowered electrophilicity ofmultiply chloride-bound olefin-palladium(II) intermediates.Consequently, much higher palladium concentrations (with its concomitantpalladium investment) are necessary to obtain volumetric productionrates of higher carbonyl compounds comparable to acetaldehyde productionrates.

An even more prohibitive disadvantage of the Wacker system formanufacturing carbonyl compounds from higher olefins is thesubstantially increased production of chlorinated organic by-products.Higher olefins are more susceptible to palladium centeredoxychlorination, which chlorinates not only at olefinic carbon atoms butalso at allylic carbon atoms. Higher aldehydes and ketones havingmethylene groups adjacent to the carbonyl group are also moresusceptible to cupric chloride mediated oxychlorination than isacetaldehyde. As a result, the productivity of the Wacker system forproducing chlorinated organic by-products increases rapidly both withincreasing number and size of hydrocarbyl substituents in the olefin.

Other, multistep manufacturing processes are typically used instead ofthe Wacker process to convert higher olefins into corresponding carbonylcompounds. For example, the manufacture of methyl ethyl ketone(2-butanone) involves the reaction of n-butenes with concentratedsulfuric acid to produce sec-butyl hydrogen sulfate and hydrolysis ofsec-butyl hydrogen sulfate to obtain 2-butanol and diluted sulfuricacid. 2-butanol is catalytically dehydrogenated to produce methyl ethylketone. The diluted sulfuric acid must be reconcentrated for recycle.

Other carbonyl compounds are instead manufactured from startingmaterials more expensive than the corresponding higher olefin. Forexample, cyclopentanone is manufactured from adipic acid instead of fromcyclopentene.

An effective method for the direct oxidation of higher olefins tocarbonyl compounds by dioxygen has been long sought in order to enablemore economical manufacturing of carbonyl compounds. Yet, in 30 yearssince the development of the Wacker system, no alternate palladium-basedsystem for the oxidation of olefins by dioxygen which avoids thedisadvantages and limitations of the Wacker system has been successfullyapplied in commercial manufacturing operation.

Systems have been proposed which use polyoxoanions, instead of cupricchloride, in combination with palladium to effect the oxidation ofolefins.

U.S. Pat. No. 3,485,877, assigned to Eastman Kodak Company (hereafter,"Eastman patent") discloses a system for converting olefins to carbonylcompounds by contacting with an agent comprising two components, one ofwhich is palladium or platinum, and the other is molybdenum trioxide ora heteropolyacid or salt thereof. This patent discloses that theso-called "contact agent" may be in an aqueous solution for a liquidphase process, but that it is advantageous and preferred to support theagent on a solid carrier for a vapor phase process in which gaseousolefin is contacted with the solid phase agent. The patent compares theoxidation of propylene with a liquid phase contact agent (in Example16), to give acetone substantially free of by-products with theoxidation of propylene in the vapor phase with a corresponding solidcontact agent (in Example 10), to give acrolein. Apparently, thebehavior of an olefin's liquid phase reaction with the disclosed aqueouscontact agent solution cannot be predicted from the behavior of theolefin's vapor phase reaction with the analogous solid contact agent.

Eastman patent discloses that, when operating in the liquid phase,heteropolyacids or their salts, and particularly phosphomolybdic acid orsilicomolybdic acid in water are preferred. Among the heteropolyacidsdisclosed, only phosphomolybdic acid and silicomolybdic acid aredemonstrated by working example. No salts of heteropolyacids are sodemonstrated. Phosphomolybdovanadic acid or salts thereof are nowherementioned in this patent.

Eastman patent also discloses the reaction in the presence of oxygen oroxygen containing gas. It also discloses periodic regeneration of thecontact agent with air. However, the use of oxygen or air isdemonstrated by working examples only for reactions of olefins in thevapor phase with solid phase contact agents.

We have found that oxygen reacts too slowly with reduced phosphomolybdicacid or silicomolybdic acid in aqueous solutions for such solutions tobe practically useful in the industrial conversion of olefins tocarbonyl compounds using oxygen or air as oxidant. In contrast, ourreduced polyoxoanions comprising vanadium in aqueous solution of thepresent invention can react rapidly with oxygen or air.

In addition, Eastman patent discloses palladium chlorides among variouspreferred palladium or platinum components for the contact agent.Palladous chloride is predominantly used among the working examples.Eastman patent also discloses that it is possible to improve the actionof the contact agent by incorporating small amounts of hydrochloric acidor ferric chloride. However, the only demonstration by working exampleadds ferric chloride in a solid phase contact agent for a vapor phasereaction (Example 19) to obtain higher reaction rates (conversion andspace time yield). No such demonstration, nor result, is given foraddition of hydrochloric acid to either a solid or a liquid phasecontact agent, nor for addition of either hydrochloric acid or ferricchloride to a liquid phase contact agent.

Belgian Patent No. 828,603 and corresponding United Kingdom Patent No.1,508,331 (hereafter "Matveev patents") disclose a system for the liquidphase oxidation of olefins employing an aqueous solution combining: a) apalladium compound; b) a reversible oxidant which has a redox potentialin excess of 0.5 volt and which is a mixed isopolyacid or heteropolyacidcontaining both molybdenum and vanadium, or a salt of said polyacid;and, c) an organic or mineral acid other than said mixed isopolyacid orheteropolyacid, which organic or mineral acid is free of halide ions andis unreactive (or at most weakly reactive) with the palladium compound.The disclosed system differs from that of Eastman patent bysimultaneously employing only certain heteropolyacids and mixedisopolyacids and adding certain other acids to the solution. Thosecertain polyacids employed contain both molybdenum and vanadium. Thosecertain other acids added are not the polyacid and are free of halideions.

Matveev patents disclose that only the certain polyacids, containingboth molybdenum and vanadium, function satisfactorily in the system asreversibly acting oxidants, wherein the reduced form of the oxidant isreacted with dioxygen to regenerate the oxidant. The patent furtherdiscloses that the polyacid used contains from 1 to 8 vanadium atoms,more preferably 6 atoms, in a molecule with molybdenum. According to thedisclosure, as the number of vanadium atoms increases from 1 to 6 theprincipal characteristics of the catalyst, such as its activity,stability, and olefin capacity, increase.

Matveev patents disclose typical heteropolyacids of a formula H_(n)[PMo_(p) V_(q) O₄₀ ], in which n=3+q, p=12-q, q=1 to 10. Matveev patentsdisclose that the catalyst is prepared, in part, by dissolving in water,oxides, salts, and/or acids of the elements forming the polyacid andthen adding to the solution, the specified other organic or mineralacid. A preferred catalyst is said to be prepared by dissolving in waterNa₃ PO₄ (or Na₂ HPO₄, or NaH₂ PO₄, or H₃ PO₄, or P₂ O₅), MoO₃ (or Na₂MoO₄, or H₂ MoO₄), V₂ O₅ (or NaVO₃), and Na₂ CO₃ (or NaOH) to form asolution, adding PdCl₂ to the solution of molybdovanadophosphoric acid,and then adding the other acid. (Sulfuric acid is the only such aciddemonstrated by working example.) It is said to be best if the totalnumber of Na atoms per atom of P is not less than 6. Heteropolyacids inthe series designated H₄ [PMo₁₁ VO₄₀ ] to H₁₁ [PMo₄ V₈ O₄₀ ] are said tobe obtained, and are said to be used in most of the working examples.(We have found that such solutions prepared according to the methodsdisclosed in Matveev patents are not actually solutions of freeheteropolyacids, as designated by formulas of the type H_(n) [PMo_(p)V_(q) O₄₀ ]. Instead, they are solutions of sodium salts of partially orcompletely neutralized heteropolyacids; that is, solutions of sodiumpolyoxoanion salts.)

According to Matveev patents, the activity and stability of the catalystis increased by the presence of certain other mineral or organic acidswhich do not react (or react only feebly) with palladium and contain nohalide ions(e.g. H₂ SO₄, HNO₃, H₃ PO₄, or CH₃ COOH). The most preferableof the above acids is sulfuric acid, which is said to increase theactivity and stability of the catalyst whilst not seriously increasingthe corrosivity of the solution. Sulfuric acid is the only acid whichappears in the working examples. Matveev patents prescribe that theamount of acid is enough to maintain the "pH" of the solution at "notmore than 3, preferably at 1.0". The working examples predominantlyrecite "pH" 1. Matveev patents indicate that with "higher pH values",the catalyst is not sufficiently stable with respect to hydrolysis andpalladium precipitation, and is of low activity in the olefinicreaction. They further indicate that with "lower pH values", the rate ofthe oxygen reaction is appreciably diminished. However, Matveev patentsdo not disclose any method for determining the "pH" of the disclosedsolutions, nor do they specify anywhere how much sulfuric acid was addedto achieve the stated "pH" value.

The disclosure of Matveev patents is generally directed towardsproviding a catalyst system having a reversibly acting oxidant (whereinthe reduced form of the oxidant can be reacted with dioxygen toregenerate the oxidant) and having an absence of chloride ions. Mineralacids which contain halide ions are specifically excluded from thecertain other acids added in the disclosed system. PdCl₂ is among thepalladium compounds used in the working examples; it is the only sourceof added chloride disclosed and is added only coincidental to theselection of PdCl₂ as the palladium source. PdCl₂ and PdSO₄ aregenerally disclosed to be equivalent palladium sources.

Matveev patents' preferred palladium concentration in the catalyst issaid to be 0.002 g-atom/liter (2 millimolar). This is the concentrationdemonstrated in most of the working examples. In Example 9 of bothBelgian and British patents, a catalyst containing a very highconcentration of heteropolyacid, 1.0 g-mole/liter, and a very highconcentration of PdCl₂, 0.5 g-atom/liter, is disclosed. This would meanthat 1.0 g-atom/liter chloride is added as part of the palladium source.The stated conclusion from this example is that the high viscosity andspecific gravity of such concentrated solutions adversely affect themass transfer conditions and make the process diffusion controlled andimpractical. The result reported for this test with 0.5 g-atom/literPdCl₂ is so poor, especially in terms of palladium activity (see Table1), as to lead one away from attempting to use the example.

The results of selected working examples reported in Matveev patents arepresented in Table 1. The examples selected are those said to use aphosphomolybdovanadic heteropolyacid in the oxidation of ethylene forwhich quantitative results are reported. Data and results to the left ofthe vertical bar in Table 1 are taken directly from the patent. Resultsto the right of the vertical bar are calculated from the reportedresults. The Example numbers are those used in Belgian 828,603.

Most working examples in Matveev patents report tests conducted in ashaking glass reactor. Typical reaction conditions in this reactor were90° C. with 4.4 psi of ethylene, and separately with 4.4 psi of oxygen.Among the examples collected in Table 1, those using the shaking glassreactor with the preferred concentrations of heteropolyacid andpalladium (Examples 1-6) gave ethylene and oxygen rates of 0.089-0.156and 0.037-0.086 (millimoles/liter)/second, respectively (see Table 1).Example 9, with 0.5 g-atom/liter PdCl₂, is said to be diffusioncontrolled; ethylene and oxygen reaction rates were 0.223 and 0.156(millimoles/liter)/second, respectively.

We have found that shaking reactors are generally poor devices formixing such gaseous reactants and liquid aqueous phases and the ratediffusion (mass transfer) of gaseous reactants into an aqueous catalystsolution for reaction is prohibitively slow in such reactors.Additionally, 4.4 psi of ethylene is relatively too low a pressure forrapid dissolution of ethylene into a aqueous catalyst solution.

                                      TABLE 1                                     __________________________________________________________________________    Examples from Belgian Patent 828,603                                          __________________________________________________________________________    Reported:                                                                                                      C.sub.2 H.sub.4                                                                   C.sub.2 H.sub.4                                                                        O.sub.2                         Ex..sup.1                                                                            [Pd].sup.3                                                                       Pd   [HPA].sup.4                                                                       HPA                                                                              % xs                                                                             temp                                                                              P.sub.C.sbsb.2.sub.H.sbsb.4                                                       rate                                                                              capacity                                                                           P.sub.O.sbsb.2                                                                    rate                            No.                                                                              Rctr.sup.2                                                                        mM source                                                                             Molar                                                                             Vq.sup.5                                                                         V.sup.6                                                                          °C.                                                                        mm Hg                                                                             W.sup.9                                                                           mole/l                                                                             mm Hg                                                                             W.sup.10                        __________________________________________________________________________    1  sg  2  PdCl.sub.2                                                                         0.3 6  25 90  230 143 0.6  230 115                             2  sg  2  PdCl.sub.2                                                                         0.3 8  35 90  230 248 0.8  230                                 3  sg  2  PdSO.sub.4                                                                         0.3 4  15 90  230 128 0.36 230 105                             4  sg  2  PdCl.sub.2                                                                         0.3 3  10 90  230 120 0.25 230 70                              5  sg  2  PdSO.sub.4                                                                         0.3 2  5  90  230 210 0.15 230 50                              6  sg  2  PdCl.sub.2                                                                         0.2 6  25 90  230 190 0.3  230 60                              6  sg  2  PdCl.sub.2                                                                         0.2 6  25 110 6 atm                                                                             900 0.3  3.5 atm                                                                           450                             9  sg  500                                                                              PdCl.sub.2                                                                         1.0 6  25 90  230 300 3.0  230 210                             10 sg  1  Pd metal                                                                           0.2 6  25 90  230 150 0.2  230 100                             12 sg  1  PdSO.sub.4                                                                         0.1 5  ?  50  230 25  0.15 230 10                              __________________________________________________________________________                      Calculated:                                                                          C.sub.2 H.sub.4                                                                    Pd             O.sub.2                                            Ex..sup.1                                                                        P.sub.C.sbsb.2.sub.H.sbsb.4                                                       rate t.f. Pd  % V                                                                              P.sub.O.sbsb.2                                                                   rate                                               No.                                                                              psi mM/s.sup.11                                                                        1/s.sup.12                                                                         TON.sup.7                                                                         red.sup.8                                                                        psi                                                                              mM/s.sup.13                      __________________________________________________________________________                      1  4.4 0.106                                                                              0.053                                                                              300 53 4.4                                                                              0.086                                              2  4.4 0.185                                                                              0.093                                                                              400 49 4.4                                                                              ?                                                  3  4.4 0.095                                                                              0.048                                                                              180 52 4.4                                                                              0.078                                              4  4.4 0.089                                                                              0.045                                                                              125 51 4.4                                                                              0.052                                              5  4.4 0.156                                                                              0.078                                                                              75  48 4.4                                                                              0.037                                              6  4.4 0.141                                                                              0.071                                                                              150 40 4.4                                                                              0.045                                              6  88.2                                                                              0.670                                                                              0.335                                                                              150 40 51.4                                                                             0.335                                              9  4.4 0.223                                                                              0.0004                                                                             6   80 4.4                                                                              0.156                                              10 4.4 0.112                                                                              0.112                                                                              200 27 4.4                                                                              0.074                                              12 4.4 0.019                                                                              0.187                                                                              150 150?                                                                             4.4                                                                              0.007                            __________________________________________________________________________     1. All examples use solutions said adjusted to pH 1 with sulfuric acid,       except Ex. 12 in which no sulfuric acid is added and the pH is not            reported.                                                                     2. Reactor type: sg = shaking glass, ss = stainless steel (method of          agitation not reported)                                                       3. Palladium concentration, millimolar (mgatom/liter)                         4. Heteropolyacid concentration, Molar (gmole/liter)                          5. Heteropolyacid said to be used, according to the formula H.sub.n           [PMo.sub.p V.sub.q O.sub.40 ], n = 3 + q, p = 12 - q                          6. Vanadium used in excess in the preparation of the HPA solution, % of q     (see footnote 5)                                                              7. Palladium turnover number per ethylene reaction = (C.sub.2 H.sub.4         capacity, moles/liter)/(Pd concentration, moles/liter)                        8. Fraction of vanadium reduced (utilized to oxidize ethylene) in ethylen     reaction = (C.sub.2 H.sub.4 capacity,mole/l)/[(total V                        concentration,gatom/l)/2], where total V concentration = [HPA](q)(1 +         fraction excess V used in HPA solution preparation)                           9. Average rate of ethylene reaction as [(milliters C.sub.2 H.sub.4 at 75     mmHg, 23°  C.)/liter solution]/minute.                                 10. Average rate of oxygen reaction as [(milliters O.sub.2 at 750 mmHg,       23° C.)/liter solution]/minute.                                        11. Rate of ethylene reaction as [millimoles C.sub.2 H.sub.4 /liter           solution/second.                                                              12. Palladium turnover frequency, {[millimoles C.sub.2 H.sub.4 /liter         solution]/second}/millimolar Pd concentration.                                13. Rate of oxygen reaction as [millimoles O.sub.2 /liter                     solution]/second.                                                        

One test in Example 6 is reported for another reactor, a stainless steelreactor, with 88.2 psi of ethylene and with 51.4 psi of oxygen, each at110° C. The method of mixing the gas and liquid phases in this reactoris not specified. Example 6 also reports results with the same catalystsystem in the shaking glass reactor. The ethylene reaction rates were0.141 (millimoles/liter)/second in the shaking glass reactor and 0.670(millimoles/liter)/second in the stainless steel reactor. The oxygenreaction rates were 0.045 (millimoles/liter)/second in the shaking glassreactor and 0.335 (millimoles/liter)/second in the stainless steelreactor. Thus, the reaction rates did not increase proportionally withthe pressure when it was increased from about 4 psi to about 90 psi. Itis well known that the diffusion rate of a reacting gas into a liquid,as well as the gas molecule concentration in the liquid phase atsaturation, is proportional to the partial pressure of the gas in thegas phase, all other factors being constant. Accordingly, the stainlesssteel reactor used for the higher pressure test of Example 6 appears tobe a poorer device for the mixing of gas and liquid phases than theshaking glass reactor used for the other test in the Matveev patents.

Typical apparent palladium turnover frequencies calculated from ethylenereaction rates and palladium concentrations reported in Matveev patents'working examples using a shaking glass reactor are all less than 0.2(millimoles C₂ H₄ /mg-atom Pd)/second. The higher pressure test at 110°C. in a stainless steel reactor in Example 6 gave the highest apparentpalladium turnover frequency of 0.335 (millimoles C₂ H₄ /mg-atomPd)/second. Although Matveev patents purport that the disclosedcatalysts are up to 30 to 100 times more active in olefin oxidation overthe Wacker catalyst, the apparent activity of the palladium catalyst inthe best example is no higher than the activity of a typical Wackerpalladium catalyst in typical process operation at comparabletemperatures. This result is obtained even though the disclosed catalystsolution is substantially free of the chloride ion concentration whichinhibits the palladium activity in the Wacker catalyst. In contrast, thepresent invention demonstrably provides palladium catalyst activitiessubstantially exceeding the activity of a Wacker palladium catalyst intypical process operation.

From Matveev patents' ethylene reaction capacities and the palladiumconcentrations, the number of palladium turnovers per ethylene reactioncapacity can be calculated (see Table 1, TON). The highest number ofturnovers obtained was 400 with the heteropolyacid containing 8 vanadiumatoms (and with 35% excess vanadium present), Example 2.

The ethylene reaction capacities of the catalyst solutions of Matveev'sworking examples appear generally to follow the vanadium content of thesolutions (see Table 1). For the tests with the preferred concentrationsof heteropolyacid and palladium and at the preferred "pH" 1 (Examples1-6), the reported ethylene reaction capacities are calculated tocorrespond to 40% to 53% of the oxidizing capacity of the vanadium(V)content of the solution, assuming two vanadium(V) centers are reduced tovanadium(IV) for each ethylene oxidized to acetaldehyde.

Example 12 of Matveev's Belgian patent reports a test with no additionof sulfuric acid. (This result was omitted from the UK patent.) Theheteropolyacid is designated H₅ [PMo₁₀ V₂ O₄₀ ] and is used at 0.1 molarconcentration with palladium sulfate at 0.1 mg-atom/liter concentration.A "pH" for this solution is not reported. The reaction is conducted at50 C. On cycling between ethylene and oxygen reactions, the rate of theethylene reaction is said to diminish constantly due to hydrolysis ofthe Pd salt. (Typical examples with sulfuric acid added, such asexamples 1-6, were reported stable to 10 or more cycles.) This resultcorresponds to Matveev's disclosure that the stability of the catalystis increased by sulfuric acid, that the amount of acid is such as tomaintain the "pH" at not more than 3, and that with higher "pH" valuesthe catalyst is not sufficiently stable against hydrolysis and palladiumprecipitation. This result reported with no addition of sulfuric acid isso poor as to lead one away from attempting to use the example.

Matveev patents also report working examples for the oxidation ofpropylene to acetone, n-butenes to methyl ethyl ketone, and 1-hexene tomethyl butyl ketone using the disclosed catalyst system. For reaction ofmixtures of n-butenes, 4.4 psi, at 90° C. in the shaking glass reactor(Example 19 in Belgian 828,603; Example 16 in UK 1,508,331), thereported reaction rate is 50 [(ml butenes at 750 mm Hg, 23°C.)/liter]/minute (corresponding to 0.037 (millimolesbutenes/liter)/second) an the capacity of the reaction solution is 0.25moles butenes/liter. The palladium concentration in the example is 2mg-atom/liter: the palladium turnover frequency is calculated 0.019(millimoles butenes/mg-atom Pd)/second; the number of Pd turnovers perbutene reaction capacity is calculated 125. The fraction of thevanadium(V) concentration of the solution reduced by the butene capacityis calculated 51%.

In contrast to the teachings of the Matveev patents, we have found thefollowing: 1) Although the Matveev patents teach that sulfuric acidincreases the activity and stability of the catalyst, we have discoveredthat substantially increased activity (olefin and oxygen reaction rates)and stability can be obtained by avoiding the presence of sulfuric acid,and of sulfate species generally; 2) Although the Matveev patents teachthat the rate of the oxygen reaction is appreciably diminished at "pH"values lower than 1, we have discovered that oxygen reaction rates canbe obtained which are orders of magnitude higher than those reported inthe patents and which are substantially undiminished in solutions havinghydrogen ion concentrations greater than 0.10 mole/liter; 3) Althoughthe Matveev patents teach that the activity and stability of thecatalyst are increased on increasing the number of vanadium atoms in thepolyacid, for example from 1 to 6, we have discovered that, at least inthe practice of the present inventions, the activity (olefin anddioxygen reaction rates) is typically invariable with the vanadiumcontent of the polyacid and the stability may be decreased on increasingthe vanadium content of the polyacid towards 6; 4) Although the Matveevpatents teach that the total number of Na atoms per atom of P be notless than 6, we have found that with the preferredpolyoxoanion-comprising catalyst solutions of the present invention,which optionally contain Na⁺ countercations, the desired acidity can beobtained while avoiding sulfuric acid by preferably keeping the numberof Na atoms per atom of P less than 6.

East German Patent No. 123,085, by some of the inventors of the Matveevpatents, discloses a chloride-free catalyst for the liquid phaseoxidation of ethylene to acetaldehyde and acetic acid that consists of asolution of a palladium salt with an anion that does not complexpalladium or does so only weakly and a heteropolyacid or isopolyacid orsalts thereof that have a redox potential greater than 0.35 V. Theaqueous solutions disclosed in the Examples contain 2.5×10⁻⁴ mole/literPdSO₄, 5×10⁻² mole/liter heteropolyacid, (specified as H₅ [P(Mo₂ O₇)₅ V₂O₆ ], H₈ [Si(Mo₂ O₇)V₂ O₆ ], or H₈ [Ge(Mo₂ O₇)V₂ O₆ ]), 5×10⁻²mole/liter CuSO₄ (omitted in Example 3), and 5×10⁻² mole/liter NaVO₃,and are said to have a "pH" of 2. Neither the method of preparation ofthe heteropolyacids in the solutions, nor the means of acidifying thesolutions to this stated "pH" is disclosed. In the Examples, thesesolutions are said to be reacted at 30° C. with ethylene at 720 mm Hgpartial pressure or at 60° C. with ethylene at 600 mm Hg partialpressure, and with oxygen at the same pressures, using a glass reactorthat can be agitated. The greatest ethylene reaction rate disclosed is44 ml ethylene reacted by 50 ml solution in 20 minutes at 60° C. withand ethylene partial pressure of 600 mm Hg, corresponding to 0.21(millimole C₂ H₄ /liter)/second and a palladium turnover frequency of0.085 (millimole C₂ H₄ /mg-atom Pd)/second. The greatest oxygen reactionrate disclosed is 10 ml oxygen reacted by 50 ml solution in 27 minutesat 30° C. with an oxygen partial pressure of 720 mm Hg, corresponding to0.005 (millimole O₂ /liter)/second.

East German Patent No. 123,085, also mentions small additions ofchloride or bromide ions act as oxidation accelerators and activate thecatalysts, with molar ratios of [Pd⁺⁺ ]:[Cl⁻ ]≦1:20 and [Pd⁺⁺ ]:[Br⁻]≦1:5 being favorable. The patent makes no other mention of chlorideaddition to the disclosed catalyst and chloride is nowhere indicated inany of the working Examples. Instead, the title of the patent, theclaims, and the disclosure elsewhere all explicitly specify achloride-free catalyst.

Additional results from some of the inventions of the Matveev patentsare reported in Kinetika i Kataliz, vol. 18(1977), pp. 380-386 (Englishtranslation edition pp. 320-326, hereafter "Kinet. Katal. 18-1").Reaction kinetic experiments are reported for the ethylene oxidationreaction with phosphomolybdicvanadic heteropolyacids in the presence ofPd(II) sulfate using a shaking reactor with circulation of the gasphase. The absolute values of the observed reaction rates are said to bequite small, and not complicated by mass-transfer processes. Most of thereported experiments are conducted at about 20° C., and this lowtemperature appears to be the principal reason the observed reactionrates are so small. Typical reaction rates reported are about 1 to12×10⁻⁴ (moles/liter)/minute, which corresponds to about 0.002 to 0.020(millimoles/liter)/second; compare to ethylene reaction rates of about0.1-0.2 (millimoles/liter)/second calculated from the results reportedfor experiments at 90° C. in Matveev patents (see Table 1). The reactionrates reported in Kinet. Katal. 18-1 are so small as to lead one awayfrom attempting to use the reported reaction conditions for anypractical production purpose.

Ethylene pressures for the reactions of Kinet. Katal. 18-1 are notreported. The ethylene concentrations are instead given, but no methodof either setting or determining the ethylene concentration ismentioned, nor is it clear whether these ethylene concentrations aresustained in solution under the reaction conditions.

Kinet. Katal. 18-1 states that solutions of phosphomolybdicvanadicheteropolyacids were synthesized by a procedure described in Zh. Neorg.Khim., vol. 18(1973), p. 413 (English translation edition pp. 216-219).This reference describes making solutions from Na₂ HPO₄, Na₂ MoO₄ ·2H₂O, and NaVO₃ ·2H₂ O at "pH" 2; the method of acidification of thesolutions of these basic salts, when stated, is with sulfuric acid.(This reference further mentions the isolation of crystallinevanadomolybdo-phosphoric acids via ether extraction of their etheraddition compounds from sulfuric acid-acidified solutions. These methodsof preparing solution vanadomolybdophosphoric acids with sulfuric acidand crystalline products by ether extraction are also described inearlier papers cited by this reference; for example, Inorg. Chem., 7(1968), p. 137.) The reaction solutions of Kinet. Katal. 18-1 are saidto be prepared from the solutions of phosphomolybdicvanadicheteropolyacids by addition palladium sulfate, dilution, and adjustmentof the pH by the addition of H₂ SO.sub. 4 or NaOH. However, thisreference does not disclose the composition of the test solutions, interms of the amounts of H₂ SO₄ or NaOH added, nor any method fordetermining the pH of the disclosed solutions.

Kinet. Katal. 18-1 reports the dependence of the ethylene reaction rateon the solution pH over the stated range 0.8 to 2.2, under the disclosedconditions with the heteropolyacid designated H₆ [PMo₉ V₃ O₄₀ ] at 0.05mole/liter, palladium at 3×10⁻³ g-atom/liter, ethylene at 1×10⁻⁴mole/liter, and 21° C. As the pH is increased towards 2, the rate of theethylene reaction is shown to decrease. From evaluation of graphicfigures in the reference, the maximum rate of ethylene reaction wasachieved over a pH range of 0.8 to 1.6, and corresponded to 0.023(millimole C₂ H₄ /liter)/second and a palladium turover frequency of 078(mole C₂ H₄ /mole palladium)/second.

Matveev reviews his studies on the oxidation of ethylene to acetaldehydein Kinetika i Kataliz, vol. 18 (1977), pp. 862-877 (English translationedition pp. 716-727; "Kinet. Katal. 18-2"). The author states (Englishtranslation edition p. 722): "The chloride-free catalyst was an aqueoussolution of one of the HPA-n, acidified with H₂ SO₄ to pH 1, in which anonhalide palladium salt (sulfate, acetate, etc.) was dissolved." (HPA-nare defined as phosphomolybdenumvanadium heteropolyacids.) Reference isthen made to the studies reported in Kinet. Katal. 18-1.

Reaction Kinetics and Catalysis Letters, vol 16 (1981), pp. 383-386reports oxidation of 1-octene to 2-octanone using a catalytic system ofPdSO₄ and heteropolyacid designated H₉ PMo₆ V₆ O₄₀ in a shaking glassreactor with 1 atm. oxygen. The heteropolyacid is said to be synthesizedas in UK 1,508,331, and used as an acidic sodium salt Na₇ H₂ PMo₆ V₆O₄₀. The catalyst solution is said to have a pH equal to 0.5-1.0, whichwas attained by the addition of H₂ SO₄. However, no results areidentified with a specific pH value. Palladium is used in concentrationsof ˜4-6 millimolar and PdSO₄ is said to give a more active catalyst thanPdCl₂. The catalyst is said to have limited stability above 80° C.,apparently due to precipitation of palladium.

Ropa Uhlie 28, pp. 297-302 (1986) (Chem Abstr. 107(1):6740r) reportsoxidation of 1-octene to 2-octanone using a solution of 0.075 Mheteropolyacid designated H_(3+n) PMo_(12-n) V_(n) O₄₀, n=6 or 8, andcontaining PdSO₄. The heteropolyacid solution was prepared from NaH₂PO₄, MoO₃, and V₂ O₅ in water by addition of NaOH, then H₂ SO₄, withadjustment of the stated "pH" to 1.

J. Organomet. Chem. 327 (1987) pp. C9-C14 reports oxidation of 1-octeneto 2-octanone by oxygen using an aqueous solution of 0.12 mole/literheteropolyacid designated HNa₆ PMo₈ V₄ O₄₀, with 0.01 mole/liter PdSO₄,with various co-solvents, at 20° C., in one-stage mode. Theheteropolyacid is said to be prepared by the method described in UK1,508,331; the "pH" of the catalyst solution is not specificallydisclosed. For the reaction, 1-octene and oxygen are contactedsimultaneously with the catalyst solution. The heteropolyacid cocatalystis said to be regenerated by treating the aqueous solution with 1 atm.O₂ at 75° C.

Reaction Kinetics and Catalysis Letters, vol 3 (1975), pp. 305-310reports the oxidation of vanadium(IV) in aqueous solutions of vanadylsulfate (V^(IV) OSO₄), 0.05-0.25 mole/liter, in the "pH" region 2.5-4.5,in the presence of small amounts of sodium molybdate in a shakerreactor, at 30° C. with 730 mmHg oxygen pressure. At "pH" values below3.0 the reaction rate is reported to decrease sharply. A heteropolyacidcomplex of molybdenum and vanadium was isolated from a reactionsolution.

Koordinatsionnaya Khimiya, vol. 3 (1977), pp. 51-58 (English translationedition pp. 39-44) reports the oxidation of reducedphosphomolybdovanadium heteropolyacids containing vanadium(IV), inaqueous solution at "pH"'s<1, at 60° C. by oxygen. Heteropolyacidsdesignated H_(3+n) [PMo_(12-n) V_(n) O₄₀ ], n=1-3, were said to besynthesized by the method of Zh. Neorg. Khim., vol. 18 (1973), p. 413(see above), and a solution of the sodium salt of the heteropolyaciddesignated n=6 was said to be prepared by dissolving stoichiometricamounts of sodium phosphate, molybdate, and vanadate in water, boilingthe solution, and acidifying it to "pH" 1. Different "pH" values for thesolutions of the reduced forms of these heteropolyacids were said to beobtained by altering the initial "pH" values of the heteropolyacidsolutions, monitored by a pH meter. The acid used for acidification andfor altering the initial "pH" values are not disclosed. Oxygen reactionrates for the reduced forms of the heteropolyacids designated n=2,3, and6 show maxima at about "pH" 3 (at about 34×10⁻³ (mole/liter)/minute; or,0.57 (millimole/liter)/second), and decline precipitously as the "pH" islowered; it becomes almost negligible for n=2 at "pH" 1.

Koordinatsionnaya Khimiya, vol. 5 (1979), pp. 78-85 (English translationedition pp. 60-66) reports the oxidation of vanadium(IV) in aqueoussolutions of vanadyl sulfate, 0.1-0.4 mole/liter, in the "pH" region2.5-4.5, in the presence of smaller amounts of molybdovanadophosphoricheteropolyacid designated H₉ PMo₆ V₆ O₄₀, in an agitated reactor, at0°-30° C., by oxygen. A weak dependence of the rate on "pH" is reported,with the rate decreasing with decreasing "pH" below about "pH" 3.5. Theaddition of Na₂ SO₄ is said to have no influence on the rate of thereaction.

Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, 1981, pp. 2428-2435(English translation edition pp. 2001-2007) reports studies of theoxidation of reduced forms ("blues") of molybdovanadophosphateheteropolyacids designated H_(3+n) [PMo_(12-n) V_(n) O₄₀ ], n=1-4,6,containing vanadium(IV), in aqueous solution at "pH" 3.0, in a glassflask with magnetically-coupled stirring of the liquid phase, at 25° C.with 2-10 kPa (0.3-1.5 psi) oxygen. Reaction rates are extremely slowunder these low temperature, low pressure conditions in this reactionmixing vessel. (From the data, reaction rates in the region <0.0001(millimoles/liter)/second are calculated.) The oxygen reaction rates ofa reduced form of the molybdovanadophosphate n=3 were measured at "pH"'s2.0,3.0, and 4.0. A maximum was observed at "pH" 3.0. Aqueous solutionsof Na salts of the heteropolyacids and the corresponding blues for theexperiments were said to be obtained as in Izvestiya Akademii Nauk SSSR,Seriya Khimicheskaya, 1980 , pp. 1469. This reference discloses thataqueous solutions of heteropolyanions were obtained by reactingstoichiometric amounts of H₃ PO₄, MoO₃, and NaVO₃ ·2H₂ O with heating inthe presence of Na₂ CO₃. (Neither the amount of Na₂ CO₃ added, theconcentration of heteropolyanion, the resulting "pH"'s, nor the completecompositions of the solutions are disclosed.) This reference furtherdiscloses the addition of vanadium(IV) in the form of VOSO₄ ·2H₂ O toproduce the heteropoly blues. The experimental solutions in thisreference are said to comprise heteropolyanion and vanadyl at "pH"1.60-2.98, buffer solution of NaHSO₄ and Na₂ SO₄ ; neither theconcentration of the buffering sulfate ions nor an accounting of theirorigin is disclosed.

Reaction Kinetics and Catalysis Letters, vol 17 (1981), pp. 401-406reports the oxidation of vanadium(IV) in aqueous solutions of vanadylsulfate, 0.02-0.4 mole/liter, in the "pH" region 2.5-4.5, in thepresence of smaller amounts of molybdovanadophosphoric heteropolyaciddesignated H₆ PMo₉ V₃ O₄₀, by the methods of Koordinatsionnaya Khimiya,vol. 5 (1979), pp. 78-85. At "pH" values below 3.0 the reaction rate isreported to decrease sharply.

J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 reports studies of thepalladium sulfate-catalyzed oxidation of 1-butene to 2-butanone (methylethyl ketone) with phosphomolybdovanadic acids both in the absence andin the presence of oxygen. These studies are reported in greater detailin Palladium and Heteropolyacid Catalyzed Oxidation of Butene toButanone, S.F. Davison, Ph.D. Thesis, University of Sheffield, 1981.These references report, as do others loc. cit., thatphosphomolybdovanadic acids are extremely complex mixtures of anions ofthe type [PMo_(12-x) V_(x) O₄₀ ].sup.(3+x)-. Crystallinephosphomolybdovanadic acids, designated H_(3+n) [PMo_(12-n) V_(n) O₄₀ ],n=1-3, prepared by the ether extraction method of Inorg. Chem., 7(1968), p. 137 were observed to be mixtures which disproportionatedstill further in the acidic media used for catalysis. Accordingly,solutions prepared by the method of UK 1,508,331 were chosen asappropriate for the catalytic reactions (see Davison Thesis, pp. 63 and77), except that stoichiometric amounts of V₂ O₅ (not excess) were used.The solutions were prepared from V₂ O₅, MoO₃, Na₃ PO₄ ·12H₂ O, and Na₂CO₃, at 0.2 M P, and acidified to "pH" 1 by addition of concentratedsulfuric acid

The reactions of J. Chem. Soc. Dalton Trans,. 1984, pp. 1223-1228 andDavison Thesis in the absence of oxygen were conducted at 20° C. and 1atm 1-butene in a mechanically shaken round-bottomed flask. Reactionsusing 5 mM PdSO₄ and 0.05 M vanadium(V) in aqueous sulfuric acid(0.03-0.2 mole/liter, depending on n) are reported to give similarinitial reaction rates for n=1-7. The reactions required ca. 30 minutesfor completion and gave 5 turnovers on Pd (stoichiometric for twovanadium(V) reduced to vanadium(IV) per 1-butene oxidized to2-butanone.). A stated intention of the work was to minimize chloridecontent; PdCl₂ is said to have similar reactivity to PdSO₄.

The reactions of J. Chem. Soc. Dalton Trans., 1984, pp. 1223-1228 andDavison Thesis in the presence of oxygen were conducted at 20° C. and 1atm of 1:1 1-butene:oxygen in a round-bottomed flask with magneticallycoupled stirring. Results are reported for the solutions used inreactions in the absence of oxygen; up to about 40 turnovers on Pd wereobtained in about 120 minutes with the heteropolyacid designated PMo₆ V₆(H₉ [PMo₆ V₆ O₄₀ ] in the journal account). An experiment is alsoreported using this heteropolyacid in 0.87 M sulfuric acid (in thejournal account it is cited as 1 M sulfuric acid and the "pH" is statedto be ca.-0.3.). The extra acid is said to be slightly detrimental: upto about 32 turnovers on Pd were obtained in about 120 minutes. Thevarious P-Mo-V co-catalysts are said to be longer lasting in the "pH"range 1-2.

U.S. Pat. Nos. 4,434,082; 4,448,892; 4,507,506; 4,507,507; 4,532,362;and 4,550,212, assigned to Phillips Petroleum Company, disclose systemsfor oxidizing olefins to carbonyl compounds comprising a palladiumcomponent, a heteropolyacid component, and additional components. U.S.Pat. No. 4,434,082 and 4,507,507 both add a surfactant and a diluent oftwo liquid phases, one of which is an aqueous phase, and one of which isan organic phase, U.S. Pat. No. 4,448,892 and 4,532,362 also both add asurfactant and a fluorocarbon. U.S. Pat. No. 4,507,506 adds cyclicsulfones (e.g. sulfolane). U.S. Pat. No. 4,550,212 adds boric acid andoptionally a surfactant. The disclosure of heteropolyacids in each ofthese patents is the same as in Matveev patents, and the heteropolyacidsdemonstrated by working examples are prepared by the same method as inMatveev patents, including acidification to "pH" 1.00 with sulfuricacid. PdCl₂ is among the palladium components exemplified. Among thedisclosed surfactants are quaternary ammonium salts and alkyl pyridiniumsalts, including chloride salts. However, cetyltrimethylammonium bromideis the only surfactant demonstrated by working example.

The working examples for olefin oxidation among the above patentspredominantly demonstrate the one-stage oxidation of individualn-butenes to 2-butanone in the presence of oxygen. U.S. Pat. No.4,434,082 and 4,507,507 demonstrate oxidation of 3,3-dimethyl-1-butene.U.S. Pat. No. 4,448,892 and 4,532,362 demonstrate the oxidation of1-dodecene. U.S. Pat. No. 4,507,506 is concerned with the one-stageoxidation of long-chain alpha-olefins and demonstrates oxidations of1-decene and 1-dodecene.

U.S. Pat. Nos. 4,720,474 and 4,723,041, assigned to CatalyticaAssociates, disclose systems for oxidizing olefins to carbonyl productscomprising a palladium component, a polyoxoanion component, andadditionally a redox active metal component (certain copper, iron, andmanganese salts are disclosed) and/or a nitrile ligand. The disclosuresemphasize the elimination of chloride from the system; the catalystsystems do not contain chloride ions except sometimes as "only traceamounts" resulting from the presence of chloride in the synthesis of thepolyoxoanion "in order to form and (or) crystallize the desiredstructure". The patents disclose that "pH" or acidity can be adjusted byvarious proton sources, such as an acid form of a polyoxoanion orcertain inorganic acids; sulfuric acid is said to be a preferred acidand is the only acid so described. The "pH" of the liquid phase is saidto be preferably maintained between 1 and 3 by the addition ofappropriate amounts of H₂ SO₄. The working examples for olefin oxidationall add H₂ SO₄ to the reaction solution, either to obtain 0.1 Nconcentration or to obtain "pH" 1.5 or 1.6.

U.S. Pat. No. 4,720,474 and 4,723,041 demonstrate by working example theoxidation of various olefins to carbonyl products: predominantly1-hexene, as well as ethylene, 1- and 2-butenes, 4-methyl-1-pentene,cyclohexene, 1-octene, and 2-octene, all in the presence of oxygen.Example XL gives initial olefin reaction rates using a catalyst solutionincluding Pd(NO₃)₂, K₅ H₄ PMo₆ V₆ O₄₀, and Cu(NO₃)₂, with H₂ SO₄ addedto "pH" 1.5, at 85° C. and 100 psig total pressure with oxygen in astirred reactor without baffles. The reported ethylene reaction rate is8.58×10⁻⁷ moles C₂ H₄ /sec ml (0.858 (millimoles/liter)/second). Thiscorresponds to a palladium turnover frequency of 0.17 (millimoles C₂ H₄/millimole Pd)/second. A slightly lower rate is reported for 1-butene.

OBJECTS OF THE INVENTION

The present invention is directed towards one or more of the followingobjects. It is not intended that every embodiment will provide all theserecited objects. Other objects and advantages will become apparent froma careful reading of this specification.

An object of this invention is to provide an effective and efficientprocess for oxidation of an olefin to a carbonyl compound. Anotherobject of this invention is to provide a catalyst solution for oxidationof an olefin to a carbonyl compound. Another object of this invention isto provide an effective and efficient process for the preparation ofcatalyst solutions for oxidation of an olefin to a carbonyl compound.

A further object of this invention is to provide an effective andefficient process for oxidation of an olefin to a carbonyl compound byone or more polyoxoanion oxidants in aqueous solution, catalyzed bypalladium. Another object of this invention is to provide an effectiveand efficient process for reoxidation of one or more reducedpolyoxoanions in aqueous solution by reaction with dioxygen. Anotherobject of this invention is to provide an effective and efficientprocess for oxidation of an olefin to carbonyl compound by dioxygencatalyzed by palladium and one or more polyoxoanion in aqueous solution.

A further object of this invention is to provide an economicallypracticable catalyst solution and process for oxidation of ethylene toacetaldehyde in an industrial acetaldehyde plant designed to operate theWacker process chemistry. Another object of this invention is to providean economically practicable process for oxidation of an olefin, otherthan ethylene, to a ketone in an industrial plant originally designed tooperate the Wacker process chemistry for the production of acetaldehyde.

A further object of this invention is to provide an economicallypracticable catalyst solution and process for oxidation of an olefindirectly to a carbonyl compound, which could not be so accomplishedpreviously due to co-production of chlorinated by-products, due toreaction rates which were too slow, or due to another reason.

A further object of this invention is to achieve any of the aboveobjectives with a less corrosive catalyst solution than the Wackercatalyst solution. Another object of this invention is to achieve any ofabove objectives while minimizing or avoiding the co-production ofhygienically or environmentally objectionable chlorinated organicby-products. Another object of this invention is to achieve any of theabove objectives in the essential absence of copper chlorides.

A further object of this invention is to achieve any of the aboveobjectives with a higher volumetric productivity (molar amount of olefinoxidized to carbonyl product per unit volume catalyst solution per unittime) than previously disclosed catalyst systems and processes. Afurther object of this invention is to achieve any of the aboveobjectives with a smaller concentration or amount of palladium catalystthan previously disclosed catalyst systems and processes. Another objectof this invention is to achieve any of the above objectives with greaterturnovers on palladium (lesser Pd cost per mole carbonyl product) thanpreviously disclosed catalyst systems and processes. Another object ofthis invention is to achieve any of the above objectives with greatercatalyst stability to long term operation than previously disclosedcatalyst systems and processes which avoid the use of copper chlorides.Another object of this invention is to achieve any of the aboveobjectives while avoiding the inverse squared rate inhibition bychloride ion concentration and the inverse rate inhibition by hydrogenion concentration which are typical of the Wacker chemistry.

A further object of this invention is to achieve any of the aboveobjectives with a greater effective utilization of the oxidationcapacity of a vanadium (V)containing polyoxoanion oxidant solution, orgreater olefin reaction capacity per unit volume, than previouslydisclosed catalyst systems and processes. Another object of thisinvention is to achieve any of the above objectives with a greatervolumetric reaction rate for the oxidation of vanadium (IV) to vanadium(V) by dioxygen (molar amount of dioxygen reacted per unit volumecatalyst solution per unit time) than previously disclosedvanadium-containing catalyst systems and processes. A further object ofthis invention is to provide an effective and efficient process foroxidation of palladium(0), particularly palladium metal, to dissolvedpalladium (II) catalyst, in order to provide and sustain palladiumcatalyst activity in the inventive catalyst system.

Still another object of this invention is to provide a method ofpreparing an aqueous catalyst solution suitable for accomplishing any ofthe above objectives.

SUMMARY OF INVENTION

The present invention provides aqueous catalyst solutions useful foroxidation of olefins to carbonyl products, comprising a palladiumcatalyst and a polyoxoacid or polyoxoanion oxidant comprising vanadium.It also provides processes for oxidation of olefins to carbonylproducts, comprising contacting olefin with aqueous catalyst solutionsof the present invention. It also provides processes for oxidation ofolefins to carbonyl products by dioxygen, comprising contacting olefinwith the aqueous catalyst solutions of the present invention, andfurther comprising contacting dioxygen with the aqueous catalystsolutions.

In certain aqueous catalyst solutions and related processes of thepresent invention, the solution has a hydrogen ion concentration greaterthan 0.10 mole per liter when essentially all of the oxidant is in itsoxidized state.

In other aqueous catalyst solutions and related processes of the presentinvention, the solution is essentially free of mineral acids and acidanions other than of the polyoxoacid oxidant and hydrohalic acids. Inother aqueous catalyst solutions and related processes of the presentinvention, the solution is essentially free of sulfuric acid and sulfateions.

In other aqueous catalyst solutions and related processes of the presentinvention, the solution further comprises dissolved olefin at aconcentration effective for oxidizing the olefin at a rate which isindependent of the dissolved olefin concentration. In other aqueouscatalyst solutions and related processes of the present invention, theaqueous catalyst solution further comprises the olefin dissolved at aconcentration effective for maintaining the activity and stability ofthe palladium catalyst for continued process operation.

In other aqueous catalyst solutions and related processes of the presentinvention, the solution further comprises dissolved olefin at aconcentration effective for oxidizing the olefin at a rate of at least 1(millimole olefin/liter solution)/second. In other processes of thepresent invention, the process comprises contacting the olefin with anaqueous catalyst solution, comprising a palladium catalyst and apolyoxoacid or polyoxoanion oxidant, in mixing conditions sufficient forthe olefin oxidation rate to be governed by the chemical kinetics of thecatalytic reaction and not be limited by the rate of olefin dissolution(mass transfer) into the solution. In other aqueous catalyst solutionsand related processes of the present invention, the aqueous catalystsolution further comprises the olefin dissolved at a concentrationeffective for the olefin oxidation rate to be proportional to theconcentration of the palladium catalyst. In other aqueous catalystsolutions and related processes of the present invention, the aqueouscatalyst solution further comprises the olefin dissolved at aconcentration effective for providing a palladium turnover frequency ofat least 1 (mole olefin/mole palladium)/second. In other aqueouscatalyst solutions and related processes of the present invention, thesolution further comprises dissolved olefin at a concentration effectivefor oxidizing the olefin at a rate which is independent of the dissolvedolefin concentration. In other aqueous catalyst solutions and relatedprocesses of the present invention, the aqueous catalyst solutionfurther comprises the olefin dissolved at a concentration effective formaintaining the activity and stability of the palladium catalyst forcontinued process operation.

In other aqueous catalyst solutions and related processes of the presentinvention, the solution further comprises chloride ions. In otheraqueous catalyst solutions and related processes of the presentinvention, the solution further comprises chloride ions at aconcentration effective for maintaining the activity and stability ofthe palladium catalyst for continued process operation. In other aqueouscatalyst solutions and related processes of the present invention, thesolution further comprises chloride ions at a concentration greater thantwice the concentration of palladium. In other aqueous catalystsolutions and related processes of the present invention, the solutionfurther comprises chloride ions at a concentration of at least 5millimole per liter.

Preferred aqueous catalyst solutions and related olefin oxidationprocesses of the present invention combine the recited features of twoor more of the above mentioned catalyst solutions and related processes.Especially preferred are aqueous catalyst solutions and relatedprocesses which combine most or all of the above features.

The present invention also provides processes for the oxidation ofvanadium (IV) to vanadium (V) comprising contacting dioxygen with anaqueous solution comprising vanadium and a polyoxoanion. In certain suchprocesses of the present invention the solution has a hydrogen ionconcentration greater than 0.10 mole per liter when essentially all ofthe oxidant is in its oxidized state. In other such processes of thepresent invention the solution is essentially free of sulfate ions. Inother such processes of the present invention the dioxygen is mixed withthe aqueous solution under mixing conditions effective to provide adioxygen reaction rate of at least 1 (millimole dioxygen/litersolution)/second.

The present invention also provides processes for the oxidation ofpalladium (0) to palladium (II) comprising contacting the palladium (0)with an aqueous solution comprising a polyoxoacid or polyoxoanionoxidant comprising vanadium and chloride ions. In certain such processesof the present invention the palladium (0) comprises palladium metal orcolloids.

The present invention also provides processes for the preparation ofacidic aqueous solutions of salts of polyoxoanions comprising vanadium,by dissolving oxides, oxoacids, and/or oxoanion salts of the componentelements (for example: phosphorus, molybdenum, and vanadium), andoptionally carbonate, bicarbonate, hydroxide and/or oxide salts, inwater, such that the resulting ratio of hydrogen ions and saltcountercations balancing the negative charge of the resultingpolyoxoanions in the solution provides a hydrogen ion concentrationgreater than 10⁻⁵ moles/liter.

We anticipate that the solutions and processes of the present inventionwill prove useful in oxidation processes other than the oxidation ofolefins to carbonyl compounds, including, for example, oxidation ofcarbon monoxide, oxidation of aromatic compounds, oxidative couplingreactions, oxidative carbonylation reactions, oxidation of halides tohalogen, and the like.

DETAILED DESCRIPTION OF THE INVENTION

Empirical and Theoretical Bases for the Invention:

We have found after extensive investigations that certain catalystsolutions and processes discussed in the background references arewholly impractical or practically unworkable for economicallypracticable commercial manufacture of carbonyl products by the oxidationof olefins. Characteristic problems we found for background catalystsolutions and processes using palladium and polyoxoanions includeinsufficient olefin oxidation reaction rates, insufficient palladiumcatalyst activity, insufficient catalyst stability for continued processoperation, and insufficient dioxygen reaction rates. The followingdiscussion outlines the results of our investigations towards solvingthese problems and our understanding of why our solutions to theseproblems are successful. We do not intend to be bound by the followingtheoretical explanations since they are offered only as our best beliefsin furthering this art.

In the oxidation of olefins to carbonyl compounds by palladium catalystsand polyoxoanion oxidants comprising vanadium, palladium appears tocatalyze the oxidation of olefins by vanadium (V) in the polyoxoanionoxidant (illustrated in reaction (12) for ethylene oxidation toacetaldehyde), where [V^(V) ] and [V^(IV) ] represent a single vanadium(V) atom and single vanadium (IV) atom in an aqueous solution ofpolyoxoanion oxidant, respectively: ##STR3##

In a subsequent step, conducted either simultaneously (one-stageprocess) or sequentially (two-stage process) to the above, vanadium (IV)in the polyoxoanion solution can be oxidized by dioxygen to regeneratevanadium (V) for the oxidation of additional olefin:

    2[V.sup.IV ]+2H.sup.+ +1/2O .sub.2 →2[V.sup.V ]+H.sub.2 O(13)

(Reactions (12) and (13) combined give the overall reaction (1) foroxidation of ethylene to acetaldehyde by dioxygen.)

Palladium appears to catalyze the oxidation of olefins by vanadium (V)in the polyoxoanion oxidant (reaction (12) by oxidizing the olefin(reaction (14), illustrated for ethylene), and then reducing vanadium(V) (reaction (15)):

    C.sub.2 H.sub.4 +Pd.sup.II +H.sub.2 O→CH.sub.3 CHO +Pd.sup.0 +2H.sup.+                                                 ( 14)

    Pd.sup.0 +2[V.sup.V ]→Pd.sup.II +2[V.sup.IV]        ( 15)

Functionally, the vanadium in the polyoxoanion solution mediates theindirect oxidation of the reduced Pd⁰ by dioxygen (reaction (15) plusreaction (13)), and functions in a manner similar to copper chloride inthe Wacker process.

We have determined that, in preferred processes of the presentinvention, under mixing conditions sufficient for the olefin oxidationrate to be governed by chemical kinetics (not limited by the kinetics ofolefin dissolution into the solution), the volumetric rate of olefinoxidation by aqueous polyoxoanion comprising vanadium (V) (reaction(12)) is first-order dependent on (proportional to) the concentration ofpalladium (II), and is substantially independent of the concentrationvanadium (V). Accordingly, the oxidation of the Pd⁰ product of reaction(14) by vanadium (V) (reaction (15)) is rapid relative to the rate ofolefin oxidation by palladium (II) (reaction (14)).

We discovered that the catalyst systems of the background referencesdiscussed above become deactivated with agglomeration of Pd⁰ tocolloidal palladium or even to precipitated solid palladium metal. Suchagglomeration and precipitation competes with the oxidation of Pd⁰ byvanadium (V) to regenerate the olefin-active Pd^(II) form (reaction(15)). Accordingly, what would have been an originally active palladiuminventory would progressively accumulate into an inactive form. Forolefin oxidation in the absence of dioxygen (as in equation (12)),essentially complete palladium catalyst deactivation would often occurin these referenced processes before effective utilization of theoxidizing capacity of the vanadium (V) content of the solution. Evenwhen most of the palladium would remain active through the olefinreaction in two-stage operation with subsequent dioxygen reaction,multiple olefin/oxygen reaction cycles resulted in a cumulative loss ofthe active palladium catalyst concentration.

The aqueous catalyst solutions of this invention have increasedstability towards deactivation because of palladium colloid or solidmetal formation. Apparently, our processes more rapidly oxidize Pd⁰ withvanadium (V) (reaction (15)) in competition with agglomeration of Pd⁰into colloids or solid palladium metal, and/or they aggressively oxidizealready agglomerated palladium (0) forms with vanadium (V), with theresult that the concentration of olefin-active Pd^(II) is maintained.Among features of the inventive solutions and related processes whichcontribute to the increased stability are the following: 1) hydrogen ionconcentrations greater than 0.10 mole/liter, 2) presence of chlorideions, especially when above a concentration coincidental to using PdCl₂as the palladium source, 3) concentrations of dissolved olefin effectivefor rapid reaction rates and sustained palladium catalyst activity, and4) essential absence of sulfate ions.

The favorable influences of hydrogen ion and chloride ion concentrationson catalyst stability are thought to be related, in part, to decreasingpalladium O/II oxidation potentials, favoring oxidation of all forms ofreduced palladium to active Pd^(II). We have also discovered thatchloride ion catalyzes the corrosive oxidation of even solid palladiummetal to soluble Pd^(II) catalyst by polyoxoanions comprisingvanadium(V). Accordingly, chloride ions can function to disfavor netaccumulation of inactive colloidal and solid metallic palladium bycatalyzing rapid regeneration of all forms of palladium(O) to activePd^(II) catalyst.

A theoretical explanation for the favorable influence of dissolvedolefin concentration on palladium catalyst stability is that dissolvedolefin is able to bind to the Pd^(O) product of olefin oxidation,stabilizing it in solution and thereby slowing its rate of agglomerationinto colloidal or metallic forms. The oft-used sulfate salts maydecrease ("salt-out") olefin solubility in the aqueous solution, therebydecreasing its ability to stabilize the palladium catalyst.

In any event, we have found that, when the concentration of chlorideions in the solution is insufficient to otherwise maintain palladiumactivity, when ethylene concentration in solution is reduced (due to lowethylene pressure in the gas phase and/or due to insufficient mixing ofthe gas and liquid phases such that the ethylene oxidation rate becomeslimited by the rate of ethylene dissolution into the solution), initialpalladium activity declines precipitously. We have determined that suchconditions are typical of the examples disclosed in Matveev patents, andcontribute to their low apparent palladium catalyst activities relativeto the present invention; a significant fraction of the loaded palladiumappears to reside in inactive forms.

Effective concentrations of dissolved olefin for sustaining thepalladium activity may be achieved when the olefin is contacted with theaqueous catalyst solution in mixing conditions sufficient for the olefinoxidation rate to be governed by the chemical kinetics of catalysis (notlimited by the rate of ethylene diffusion into the solution), and arefurther enhanced by raising the concentration of olefin in the olefinicphase (as in raising the partial pressure of gaseous olefins). Mixingconditions sufficient for the olefin oxidation rate to be governed bythe chemical kinetics of the catalytic reaction are established when thereaction rate is governed by chemical characteristics of the catalystsolution, such as its palladium(II) catalyst concentration, andindependent of moderate variations in the phase mixing efficiency. Whenmixing conditions are insufficient, the dissolved olefin concentrationin the bulk catalyst solution is depleted by reaction, and the olefinoxidation rate becomes determined by the rate of dissolution (masstransfer) of the olefin into the catalyst solution. When mixingconditions are sufficient, the dissolved olefin concentration approachesthe phase partitioning limit (the solubility of the olefin in thesolution) and this limit is increased in proportion to the olefinconcentration in the olefinic phase. For each combination of olefin,olefin concentration in the olefinic phase, precise catalyst solutioncomposition, and reaction temperature, sufficient mixing requirements ina given reactor device can be established by observing reaction ratesgoverned by chemical kinetic parameters. For ethylene, with preferredaqueous catalysts of the present invention, the ethylene oxidationreactor of a Wacker plant, operated at its typical pressure andtemperature provides sufficient concentrations of dissolved ethylene.

In comparison to the inventive catalyst solutions and processes, thecatalyst systems and processes of background references using catalystscomprising palladium and polyoxoanion components have generally poorpalladium catalyst activity. The background references typically utilizemuch higher high palladium catalyst loadings to compensate for lowpalladium activity, and even then do not report acceptable volumetricolefin oxidation rates. A higher palladium concentration results in alesser number of palladium turnovers (moles olefin reacted/molepalladium present) to react an amount of olefin. Accordingly, thepalladium in the systems of the background references is used relativelyinefficiently; that is, more palladium is used for the production of agiven amount of carbonyl product. Since palladium is a very costlycatalyst solution component, this places an economic burden oncommercial utilization of the background reference processes.

A convenient measure of palladium catalyst activity is the palladiumturnover frequency, (moles olefin reacted/mole palladium)/unit time.Palladium turnover frequencies for ethylene oxidation determined fromdata presented in the background references, are substantially less than1 (mole ethylene/mole Pd)/second, often less than 0.1 (moleethylene/mole Pd)/second. Aqueous catalyst solutions and processes ofthe present invention can provide palladium turnover frequencies greaterthan 1 (mole ethylene/mole Pd)/second, generally greater than 10 (moleethylene/mole Pd)/second. Palladium turnover frequencies greater than100 (mole ethylene/mole Pd)/second have even been achieved with thepresent invention.

Similarly improved palladium catalyst activities are also obtained forolefins other than ethylene. Each olefin will have its own intrinsicrate of reaction with the Pd^(II) in a given aqueous catalyst solution,and these rates are influenced by the conditions of the olefin oxidationprocess using the solution. However, the relative reaction rates ofdifferent olefins with various palladium catalyst solutions undervarious reaction conditions generally follow the same qualitative order.

The poor palladium catalyst activity of the catalyst systems of thebackground references can be attributed in part to the extent ofdeactivation of the active palladium catalyst into inactive forms; afraction of the palladium load resides in colloidal or solid metallicforms with little or no activity. To that extent, the features of thecatalyst solutions and related processes of the present invention whichcontribute to improved palladium catalyst stability, as recited above,also contribute to better apparent palladium catalyst activity.

Aqueous catalyst solutions and related processes of the presentinvention were also discovered to provide higher intrinsic palladium(II)activity than the catalyst systems and processes of backgroundreferences. (Intrinsic palladium(II) activity can be determined byobserving initial reaction rates under conditions when all the palladiumloaded is initially present as olefin-active palladium(II); that is, inthe absence of any accumulation of inactive forms.) Among the featuresof the inventive solutions and related processes which contribute toincreased intrinsic palladium(II) activity are: 1) hydrogen ionconcentrations greater than 0.10 mole/liter, 2) mixing conditionssufficient for the olefin oxidation rate to be governed by the chemicalkinetics of the catalysis, not limited by the rate of olefin dissolutioninto the solution, 3) increased concentrations of dissolved olefin insolution provided by increasing its solubility (for example, byincreasing the pressure of gaseous olefins), and 4) essential absence ofsulfate ions. Surprisingly, the presence of chloride ions may alsocontribute to higher palladium activity, depending on the chlorideconcentration and the hydrogen ion concentration. Particularly, athydrogen ion concentrations less than about 0.10 moles/liter, thepresence of an effective concentration of chloride ions can increasepalladium activity over the level with no chloride present.

In acidic aqueous solutions comprising palladium(II) (containing nocoordinating ligands or anions other than water), Pd^(II) exists inaqueous solution predominantly as its hydrolytic forms:tetraaquopalladium dication, Pd(H₂ O)₄ ²⁺, aquated palladium hydroxide,Pd(OH)₂ (H₂ O)₂ and solid phase palladium oxide which may be hydrated.These forms are interconverted by the following equilibria:ps

    Pd.sup.II (H.sub.2 O).sub.4.sup.2+ ⃡Pd.sup.II (OH).sub.2 (H.sub.2 O).sub.2 +2H.sup.+                               (16)

    Pd.sup.II (OH).sub.2 (H.sub.2 O).sub.2 ⃡Pd.sup.II O·nH.sub.2 O+(3-n) H.sub.2 O                     (17)

The two step-wise acid dissociation constants of reaction 16 have notbeen resolved (Pd^(II) (OH)(H₂ O)₃ ⁺ has not been detected), and thepK_(a) of reaction 16, as written, is reported to be 2 in water, at ornear zero ionic strength.

We have found that, contrary to the teaching of Matveev patents, theactivity of the catalyst solution, specifically its volumetric olefinoxidation reaction rate, is independent of the vanadium content ofphosphomolybdovanadate heteropolyacids, when tested at the same hydrogenion concentration greater than 0.10 mole/liter, in the absence ofsulfuric acid and sulfate ions, under mixing conditions sufficient forthe rate to be governed by the chemical kinetics of catalysis. Since thechemical kinetics are first-order dependent on the concentration of thePd^(II), these findings indicate that under these conditions, theolefin-active Pd^(II) is not coordinated by phosphomolybdovanadateheteropolyanions (since its reactivity does not depend on the identityof heteropolyanions). Accordingly, it appears that under theseconditions, the olefin-active Pd^(II) exists in solution astetraaquopalladium, Pd^(II) (H₂ O) ₄ ²⁺.

We further discovered that (in the effective absence of chloride ion)the rate of palladium catalyzed olefin oxidation in the polyoxoanionsolution is highest with solutions having hydrogen ion concentrationsgreater than 0.1 mole/liter, and rates decrease substantially as thehydrogen ion concentration of the solution is decreased to 0.1mole/liter and less. This indicates that the dicationictetraaquopalladium, Pd^(II) (H₂ O)₄ ²⁺ is the most active form ofpalladium(II) under these conditions, and that as the hydrogen ionconcentration of the solution is decreased to 0.1 mole/liter and less,an increasing fraction of the palladium(II) present as Pd^(II) (H₂ O)₄²⁺ is converted to less active (lower positively charged and lesselectrophilic) hydroxo-and/or oxo-forms by deprotonation of coordinatedwater, via equilibria such as reaction (16)(17). These hydrolytic formsare apparently less active due to their lower positive charge anddecreased electrophilicity at Pd^(II). Therefore, it is quite desirableto utilize polyoxoanion solutions having hydrogen ion concentrationsgreater than 0.10 mole/liter.

Hydrogen ion concentrations of polyoxoanion solutions, as recitedherein, refer to the hydrogen ion concentration when essentially all thepolyoxoanion is fully oxidized, which is when essentially all thevanadium is vanadium(V). The hydrogen ion concentrations of preferredpolyoxoanion solutions often change when they are reduced, and thesechanges are not yet completely understood and predictable. Somesolutions having hydrogen ion concentrations greater than 0.10mole/liter when fully oxidized were discovered to have hydrogen ionconcentrations less than even 0.01 mole/liter after being fully reducedby olefin oxidation. Since the theoretical equation for olefin oxidation(reaction (12)) potentially adds hydrogen ions into solution, thedecreased hydrogen ion concentration in these reduced solutionspresumably results from some re-equilibration of the initially producedvanadium(IV)-polyoxoanion species with water which consumes even morehydrogen ions than are potentially released by reaction (12).

None-the-less, olefin oxidation reactions using such an oxidizedsolution were found to proceed with an essentially constant ratecharacteristic of the initial hydrogen ion concentration up to highconversion of the vanadium(V) when provided with a sufficientcombination of palladium concentration, dissolved olefin concentration,temperature, and other reaction conditions to achieve a relatively rapidolefin reaction. In contrast, when the reaction conditions were notsufficient to provide such a relatively rapid olefin reaction, thereaction rate would decelerate with vanadium(V) conversion, commensuratewith a concomitant decrease in hydrogen ion concentration. Apparently,when sufficient reaction conditions are provided for relatively rapidolefin reaction, high vanadium(V) conversion occurs before a significantdecrease in hydrogen ion concentration can occur by what must berelatively slow re-equilibration of the initially producedvanadium(IV)-polyoxoanions. In contrast, when the reaction conditionsare not sufficient to provide relatively rapid olefin reaction, thisslow re-equilibration of the initially producedvanadium(IV)-polyoxoanions can occur while they are relatively slowlyformed and the reaction rate decelerates concomitant with the decreasinghydrogen ion concentration.

Background references for the oxidation of olefins with systems usingpalladium and vanadium-containing polyoxoacids generally teach thatPdCl₂ and PdSO₄ are equivalent palladium catalysts. PdSO₄ completelyionically dissociates in water to sulfate ions and one or morehydrolytic forms of Pd^(II), as governed by hydrogen ion concentration.Accordingly, one would be led to conclude that when PdCl₂ is added inthe systems of the background references, chloride is similarlydissociated to give the same hydrolytic form(s) of Pd^(II). However, thebackground references do not report the addition of chloride ions at aconcentrations in excess of that coincidental to providing PdCl₂.Indeed, the background references generally promote that chloride-freesystems are most desirable. The Wacker system, with its higherconcentrations of chloride, typically about 2 moles/liter, exhibits asevere, second order inhibition of the ethylene oxidation rate bychloride ion concentration.

Inventive aqueous catalyst solutions and related processes, by having aneffective concentration of chloride ions, give substantially improvedcatalyst stability with little to only moderate inhibition of theintrinsic Pd^(II) activity. Moreover, since a greater fraction of loadedpalladium can be maintained in the active Pd^(II) form, greaterproductivity can be obtained from the total palladium load in continuousoperation by the addition of an effective concentration of chlorideions.

In tested embodiments with hydrogen ion concentrations less that 0.1mole/liter, the presence of chloride ion at 5 millimoles/liter does notinhibit Pd^(II) activities to any important degree. With chloride ion at25 millimoles/liter, Pd^(II) activities were within 40≧60% of those inthe absence of chloride ions, and still about 100 times greater than fora typical Wacker catalyst system under comparable conditions.

Even more surprisingly discovered, as the hydrogen ion concentration isdecreased below 0.1 moles/liter, a region where Pd^(II) activity in theabsence of chloride ions decrease substantially, Pd^(II) activity in thepresence of an effective concentration of chloride ions can besubstantially maintained. Said another way, intrinsic Pd^(II) activityin the presence of chloride can exceed Pd^(II) activity in the absenceof chloride. In tested embodiments with hydrogen ion concentrationsabout 0.01 mole/liter, Pd^(II) activity in the presence of 25millimoles/liter chloride ion were about 5 times greater than thosewithout chloride.

When chloride ions are added to solutions of acidic solutions of Pd^(II)in water, a series of aquated chloride complexes are formed as thechloride ion concentration is increased. Where the acidity is such toprovide Pd^(II) (H₂ O)₄ ²⁺ as the hydrolytic form, the series is asfollows (in each of the following equilibria a chloride ion is added anda water is lost, to the right as written):

    Pd(H.sub.2 O).sub.4.sup.2+ ⃡PdCl(H.sub.2 O).sub.3.sup.+ ⃡PdCl.sub.2 (H.sub.2 O).sub.2 ⃡PdCl.sub.3 (H.sub.2 O).sup.- ⃡PdCl.sub.4.sup.=                    ( 18)

As the acidity of a solution is decreased, each of the complexescontaining coordinated water can dissociate a hydrogen ion to leave acomplex of coordinated hydroxide. With the successive replacement ofcoordinated water in Pd(H₂ O)₄ ²⁺ by chloride ions (equation (18)), thepositive charge on the palladium complex is decreased and the pK_(a) fordeprotonation of remaining coordinated water is increased. This increasein pK_(a) by chloride coordination appears sufficient so that thechloro-aquo species formed in the presence of moderate amounts ofchloride, are not significantly deprotonated to chloro-hydroxo speciesas the hydrogen ion concentration is decreased to at least 0.01millimoles/liter. Thereby, the Pd^(II) catalyst activity of thesechloride-bound catalysts at hydrogen ion concentrations greater than 0.1mole/liter can be substantially maintained on decreasing the hydrogenion concentration to at least 0.01 millimoles/liter. Further, thechloro-aquo species appear substantially more active for olefinoxidation than hydroxo-aquo species (such as Pd^(II) (OH)₂ (H₂ O)₂)formed when Pd(H₂ O)₄ ²⁺ is deprotonated as the hydrogen ionconcentration is decreased towards 0.01 millimoles/liter.

We have also discovered that in using the inventive chloride-comprisingcatalyst solutions for the oxidation of olefins, chlorinated organicby-products are not formed or are formed in amounts insignificantrelative to the amounts formed with the Wacker catalyst system.Apparently, the essential absence of copper ions in preferred catalystsolutions which include chloride, substantially avoids significantoxychlorination of organics.

The polyoxoanion in the solutions and processes of the present inventionappears to provide two functions which are not provided with vanadiumalone in aqueous solution. First, the polyoxoanion solution provides anenvironment for dissolution of suitably high concentrations of vanadium.In acidic aqueous solutions with hydrogen ion concentrations comparableto preferred solutions of the present invention, vanadium(V) aloneexists predominantly as the pervanadyl ion, VO₂ ⁺ _(aq), whosesolubility is limited; at saturation, it deposits solid V₂ O₅. Likewise,vanadium(IV) alone exists predominantly as the vanadyl ion, VO²⁺ _(aq),which saturates with respect to insoluble reduced vanadium oxides. Incontrast, polyoxoanions comprising vanadium can provide vanadiumsolubilities to much higher concentrations, such as the decimolar tomolar level concentrations of vanadium utilized in preferred solutionsand processes of the present inventions.

Second, the polyoxoanion solution appears to enable suitably rapidreaction of vanadium(IV) with oxygen, to regenerate vanadium(V)(reaction (13)). Although pervanadyl ion is capable ofpalladium-catalyzed oxidation of olefins, in a reaction similar toreaction (12), vanadyl ion alone reacts only very slowly with dioxygento regenerate pervanadyl. In contrast, in our preferred polyoxoanionsolutions, polyoxoanions comprising vanadium(IV) react very rapidly withdioxygen, thereby providing preferred processes of the presentinvention. Moreover, when vanadyl(IV) ion is present in the polyoxoanionsolution, it too can react rapidly with dioxygen. Preferredpolyoxoanions comprising vanadium, which enable particularly rapidoxidation of vanadium(IV) to vanadium (V), further comprise phosphorusor molybdenum. Particularly preferred polyoxoanions further compriseboth phosphorus and molybdenum.

Our processes, which include reaction of preferred polyoxoanionsolutions comprising vanadium(IV) with dioxygen, can proceed withvolumetric dioxygen reaction rates of at least 1 (millimoledioxygen/liter solution)/second) and up to multiplicatively greaterrates than those in background references. Improved volumetric dioxygenreaction rates can be achieved, in part, by operating thevanadium(IV)-dioxygen reaction process under more efficient gas-liquidmixing conditions. It was surprisingly discovered that these evenimproved rates are still limited by the diffusion (mass transfer) ofdioxygen into the aqueous solution, so that still more rapid rates couldbe achieved under still more efficient gas-liquid mixing conditions.

The air reactors in a Wacker-type acetaldehyde manufacturing plantprovide efficient gas-liquid mixing for achieving the commerciallypracticable dioxygen reaction rates provided by the present invention.The dioxygen reaction rates so achieved are suitable for utilization inmanufacturing a carbonyl product using a Wacker-type manufacturingplant.

We also surprisingly discovered that the presence of sulfate salts inaqueous polyoxoanion solutions, such as those of background referenceswhich are prepared by acidification using sulfuric acid, results inslower volumetric dioxygen reaction rates. Rates of reaction which arelimited by diffusion (mass transfer) of a gas into a solution are apositive function of the solubility of the gas in the solution. Thepresence of sulfate salts may decrease ("salts-out") the solubility ofdioxygen in aqueous catalyst solutions and so decrease volumetricdioxygen reaction rates, but there may be other explanations. In anycase, in comparisons under the same mixing and reaction conditions,polyoxoanion solutions comprising vanadium(IV) react with dioxygen atgreater volumetric reaction rates when the solution is essentially freeof sulfate ions.

Background references teach that volumetric reaction rates of reducedpolyoxoanion solutions with dioxygen decrease as the recited "pH"s ofsolutions are decreased towards 1. Matveev patents specifically teachthat with "lower pH values" (their preferred "pH" is said to be 1), therate of the oxygen reaction is appreciably diminished. In contrast, wehave found that our solutions and processes oxidize vanadium(IV) inaqueous solution by dioxygen at substantially undiminished volumetricdioxygen reaction rates over a range of hydrogen ion concentrationsextending substantially greater than 0.1 mole/liter. Consequently, weare able to use high hydrogen ion concentrations (e.g. greater than 0.1mole/liter) to promote palladium catalyst stability and olefin oxidationactivity and yet maintain exceptional polyoxoanion oxidant regenerationrates.

Catalyst Solution and Process Description:

The following is additional description of the aqueous solutions of thepresent invention and their use in processes for the oxidation ofolefins to carbonyl products:

Olefins:

Olefins suitable for oxidation according to the process of thisinvention are organic compounds having at least one carbon-carbon doublebond, or mixtures thereof. Examples of suitable olefins are compoundsrepresented by the formula RR'C═CHR" wherein R, R', and R" eachrepresents a hydrogen atom, a hydrocarbyl substituent, or a heteroatomselected from the group halogen, oxygen, sulfur, or nitrogen, which maybe the same or different, and which may be connected in one or more ringstructures. Although there is no inherent limit on the size of thehydrocarbyl substituents R, R', or R", they suitably may be linear,branched, or cyclic as well as mononuclear or polynuclear aromatic. Thehydrocarbyl substituents described may be C₁ to C₂₀, although C₁ to C₄are especially preferred. Each hydrocarbyl substituent may also containone or more heteroatoms of halogen, oxygen, sulfur, or nitrogen.

The olefins themselves may be either cyclic or acyclic compounds. If theolefin is acyclic, it can have either a linear structure or branchedstructure, and the carbon-carbon double bond may be either terminal("alpha-olefins") or non-terminal ("internal olefins"). If the olefin iscyclic, the carbon-carbon double bond may have either one, both, orneither of the carbon atoms of the double bond within the cycle. If theolefin contains more than one carbon-carbon double bond, the doublebonds may be either conjugated or unconjugated.

Examples of suitable olefins are ethylene, propylene, 1-butene, 2-butene(cis and trans), 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene,1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, 1-eicosene,1-vinylcyclohexane, 3-methyl-1-butene, 2-methyl-2-butene,3,3-dimethyl-1-butene, 4-methyl-1-pentene, 1,3-butadiene,1,3-pentadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene,cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclododecene,1,5-cyclooctadiene, 1,5,9-cyclododecatriene. Preferred olefins areethylene, propylene, 1-butene, cis-2-butene, trans-2-butene,3-methyl-1-butene, 2-methyl-2-butene, 4-methyl-1-pentene, cyclopentene,and cyclohexane. Mixtures of olefins may also be oxidized. Preferredmixtures of olefins comprise olefins which yield a common carbonylproduct on oxidation, for example, mixtures of 1-butene, cis-2-butene,and/or trans-2-butene for the production of 2-butanone, and mixtures of3-methyl-1-butene and 2-methyl-2-butene for the production of3-methyl-2-butanone.

The olefins introduced in the process of the present invention may bediluted by other compounds which are inert towards the oxidationreaction condition, for example, by dinitrogen, carbon dioxide, waterand saturated aliphatic compounds such as methane, ethane, propane,butane, cyclohexane, and the like. For example, 1-butene, cis-2-butene,and/or trans-2-butene for the oxidation process may be provided inadmixture with butane; cyclohexane may be provided in admixture withcyclohexane and/or benzene.

With gaseous olefins, the process involves mixing a gaseous olefinicphase with the aqueous catalyst solution. With olefins which are liquidunder the reaction conditions, the process typically involves mixing anolefinic phase with the aqueous catalyst solution. Surfactants and/orcosolvents may optionally be used to increase the solubility of theolefin in the aqueous solution, or to increase the efficiency ofdiffusion (mass transfer) of olefins into the aqueous catalyst solution,or both. See for example, the surfactants and cosolvents disclosed inU.S. Pat. Nos. 4,434,082 and 4,507,507. Alternatively, cosolvents whichmiscibilize otherwise separate olefinic and aqueous phases may be added.See for example, the cyclic sulfone cosolvents disclosed in U.S. Pat.No. 4,507,506.

Dioxygen:

Dioxygen may be introduced into processes of the present invention asoxygen, air, or mixtures thereof (enriched air). The dioxygen may be inadmixture with an inert gas, for example, dinitrogen, carbon dioxide,water vapor. The dioxygen is typically added to the process at a partialpressure at least equal to its partial pressure in air at one atmospherepressure.

Carbonyl Products:

The carbonyl products of the present invention are organic compoundscomprising at least one carbon-oxygen double bond: aldehydes, ketones,carboxylic acids, and derivatives thereof. Acetaldehyde is the initialcatalytic reaction product of ethylene oxidation. Ketones are typicallythe initial catalytic reaction products of oxidations of higher olefins.For olefins which have double-bond positional isomers, mixtures ofisomeric ketones may be obtained. For example, 1-hexene may yieldmixtures of 2-hexanone and 3-hexanone.

The process of the present invention is highly selective to the initialcatalytic reaction products (acetaldehyde and ketones); they are formedwith selectivities typically higher than 80%, usually higher than 90%,and often higher than 95%. These carbonyl products may be separated inhigh yield from the reaction solution. Alternatively, the initialproducts may be further oxidized by continued exposure to the oxidizingreaction conditions, especially the dioxygen reaction for regeneratingthe oxidant. Typically, the initial carbonyl products are oxidized tocarboxylic acids by such continued exposure. For example, acetaldehydemay be converted to acetic acid, and cyclohexanone may be converted toadipic acid.

Palladium Catalysts:

The palladium catalyst of the present invention may comprise anypalladium containing material which is suitable for oxidation of olefinsunder the oxidation process conditions. The active palladium catalyst inthe solution may be provided to the solution as palladium(0), forexample palladium metal, or a palladium compound. Palladium(II) saltsare convenient sources of palladium catalyst. Preferred palladium(II)salts include palladium acetate (Pd(CH₃ CO₂)₂), palladiumtrifluoroacetate (Pd(CF₃ CO₂)₂), palladium nitrate (Pd(NO₃)₂), palladiumsulfate (PdSO₄), palladium chloride (PdCl₂), disodiumtetrachloropalladate (Na₂ PdCl₄), dilithium tetrachloropalladate (Li₂PdCl₄), and dipotassium tetrachloropalladate (K₂ PdCl₄).

It is preferred that palladium catalyst is dissolved in the aqueoussolution. When palladium(0) metal is the palladium source, it isdissolved by oxidation to palladium(II) by the polyoxoanion oxidant.This oxidative dissolution of palladium(0) to give active palladiumcatalyst generally requires heating of the mixture, and is acceleratedin the present invention by the presence of chloride ions. Palladium(0)may be provided as palladium metal or colloids. Palladium metal may beprovided as bulk metal (shot, wire, foil), palladium sponge, palladiumblack, palladium powder, and the like.

Since palladium catalyst activity depends on such factors as theidentity of the olefin, olefin concentration dissolved in aqueoussolution, chloride ion concentration, hydrogen ion concentration,sulfate ion concentration, temperature, and other reaction conditions,the palladium concentration in the aqueous catalyst solution can vary ina broad range, typically within 0.01 to 100 millimoles/liter. Althoughthe preferred palladium concentration will depend on other such aspectsof the embodiment, it can be readily determined for each application.The ratio of the molar palladium concentration to the molar polyoxoanionconcentration will be an effective amount but less than 1. Preferredpalladium concentrations are generally 1/10 to 1/10000 of theconcentration of the polyoxoanion. For oxidation of gaseous olefins,such as ethylene, propylene, and butenes, preferred palladiumconcentrations are typically 0.1 to 10 millimolar. The present inventionenables practical ethylene oxidation reactions using palladium catalystconcentrations less than 1.0 millimolar.

Polyoxanion and Polyoxoacid Oxidants:

Polyoxoanions, and corresponding polyoxacids, utilized as oxidants inthe present processes, are isopolyoxoanions and heteropolyoxoanionscomprising vanadium. A treatise on polyoxanion compositions, structures,and chemistry is found in Heteropoly and Isopoly Oxometallates by M. T.Pope, Springer-Verlag, N.Y., 1983, which is incorporated by referenceentirely. Polyoxoanions comprising vanadium have at least one vanadiumnucleus and at least one other metal nucleus, which may be anothervanadium nucleus or any other metal nucleus which combines with vanadiumin an oxoanion composition.

Examples of suitable polyoxoanions and polyoxoacids are represented bythe general formula:

    [H.sub.y X.sub.a M.sub.b M'.sub.c V.sub.x O.sub.z ].sup.m-

wherein:

H is proton bound to the polyoxoanion;

V is vanadium;

O is oxygen;

X is selected from the group consisting of boron, silicon, germanium,phosphorus, arsenic, selenium, tellurium and iodine--preferablyphosphorus;

M and M' are the same or different and are independently selected fromthe group consisting of tungsten, molybdenum, niobium, tantalum, andrhenium--preferably at least one of M and M' is molybdenum;

y,a,b,c, and m are individually zero or an integer (a is zero forisopolyoxoanions and mixed isopolyoxoanions, or a is an integer forheteropolyoxoanions);

x, and z are integers; and,

b+c+x is greater than or equal to 2.

Preferred polyoxoanions are the so-called Keggin heteropolyoxoanionsrepresented by the above general formula, additionally defined wherein:

a is one,

b+c+x is 12;

z is 40.

Most preferred are Keggin heteropolyoxoanions and heteropolyacidscomprising phosphorus, molybdenum, and vanadium(phosphomolybdovanadates), represented by the following formula when inthe oxidized state:

    [H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-

wherein:

x and y are integers;

0>x≦12; and,

0≦y≦(3+x).

More specifically, 0≦y≦(3+x) for polyoxoanion species and 0≦y≦(3+x) forpolyoxoacid species. Except when a polyoxo species is completelydeprotonated (i.e.,y=0) or completely protonated (i.e., y=(3+x)), it isboth a polyoxoanion species and a polyoxoacid species. However, protonsdissociated into solution may also be considered in designating asolution as comprising a polyoxoacid, even though all the polyoxospecies present may be fully deprotonated in the solution. The Kegginphosphomolybdovanadates have been found to be anions of very strongacids, and are believed never to be fully protonated in aqueoussolution.

Preferred phosphomolybdovanadate solutions have phosphorus, molybdenum,and vanadium present in relative molar amounts approximating thecomposition of the Keggin heteropolyoxoanions; that is ([Mo]+[V])≅12[P]. However, solutions having an excess of one or two componentsover these ratios are also intended. In particular, excess phosphoricacid or phosphate salt may be present. It is also intended that theKeggin phosphomolybdovanadate solutions may optionally comprise excessvanadium (for example, as VO₂ ⁺) over the Keggin ratios.

The net negative charge of the polyoxoanions is balanced bycountercations which are protons and/or salt cations. When only protonsare present as countercations (when y=(3+x) for the Kegginphosphomolybdovanadic acid), one has a "free acid" polyoxoacid. When oneor more salt cations are present as countercations, in place of protons,one has a polyoxoanion salt, also called a salt of the polyoxoacid. Whenboth protons and salt cations are present, one has a partial salt of thepolyoxoacid; the free polyoxoacid is partially neutralized.

Suitable salt countercations are those which are inert, or in some wayadvantageous (for example, Pd(H₂ O)₄ ²⁺, VO₂ ⁺), under the reactionconditions. Preferred salt countercations are alkali metal cations andalkaline earth cations which do not precipitate insoluble polyoxoanionsalts; for example: lithium, sodium, potassium, beryllium, and magnesiumcations, or mixtures thereof. Most preferred are lithium (Li⁺), sodium(Na⁺), and magnesium (Mg²⁺) cations. Mixtures of salt countercations maybe present.

The Keggin phosphomolybdovanadates exist in aqueous solution asequilibrium mixtures of anions varying in vanadium and molybdenumcontent (varying in x). Moreover, for each value x such that 1>×>11,there are a number of positional isomers for the placement of thevanadium and molybdenum in the Keggin structure: for x=2 there are fiveisomers, for x=3 there are 13 isomers, for x=4 there are 27 isomers, andso on. Each of these compositional and isomeric species has its own aciddissociation constants which determine the extent to which it isprotonated at a given hydrogen ion concentration is solution. (That is,each compositional and isomeric species can have its own average y valuein a given solution.) Accordingly, the compositions of aqueous Kegginphosphomolybdovanadate solutions are not generally easily characterizedin terms of a their component species [H_(y) PMo.sub.(12-x) V_(x) O₄₀].sup.(3+x-y)- and their individual concentrations.

The present inventors have adopted a simplified, yet definitive, methodof designating the elemental constitution of solutions containing Kegginphosphomolybdovanadate free acids or alkali metal salts in the oxidizedstate, in terms of the general formula:

    {A.sub.p H.sub.(3+n-p) PMO.sub.(12-n) V.sub.n O.sub.40 }

wherein:

A is an alkali metal cation (Li⁺, Na⁺);

the designated concentration of the solution is its phosphorusconcentration, usually reported in moles/liter (molar, M);

phosphorus, molybdenum, vanadium are present in the concentration ratiosdefined by n, and 0<n<12;

alkali metal is present in solution in a concentration ratio tophosphorus defined by p, and 0≦p≦(3+n).

Accordingly, the negative charge of the designated Keggin formula infully deprotonated form, 3+n, is balanced in solution by p+qmonocations. Since this designation refers to a mixture ofpolyoxoanions, n and p may be non-integral.

This designation completely defines the elemental constitution of anaqueous solution. A given elemental constitution will have onethermodynamic equilibrium distribution of species comprising itscomponent elements. When the phosphorus, molybdenum, and vanadium inthese solutions are predominantly present in Keggin heteropolyanions offormula [H_(y) PMo.sub.(12-x) V_(x) O₄₀ ].sup.(3+x-y)- (which is usuallythe case in the preferred solutions of the present invention), then n isapproximately equal to the average value of x among the distribution ofspecies. The concentration of free hydrogen ions in such a solution isapproximately the concentration of phosphorus multiplied by thedifference between p and the average value of y among the distributionof species. When the phosphomolybdovanadates are the only acids insolution, the acidity of the solution can be set by thephosphomolybdovanadate concentration, its identity (n), and the ratio ofalkali cations (p) to hydrogen ions (3+n-p).

Preferred phosphomolybdovanadate solutions following this method ofdesignation have 0<n<12. Especially preferred solutions have 2<n<6.

The concentration of the polyoxoanion can be varied over a broad range,typically within 0.001 to 1.0 moles/liter. Preferred concentrationsdepend strongly on the composition of the polyoxoanion, the specificapplication, and the reaction conditions. For oxidation of gaseousolefins, such as ethylene, propylene, and butenes, preferredpolyoxoanion concentrations are typically 0.1 to 1.0 molar.

The polyoxoanions can be provided to the aqueous catalyst solution bydissolving prepared polyoxoanion solids (free acids or salts) or bysynthesis of the polyoxoanion directly in the aqueous solution fromcomponent elemental precursors. Suitable polyoxoanion solids andpolyoxoanion solutions can be prepared by methods in the art, such as inthe background references cited in the section Background of theInvention. For those solutions and related processes of the presentinvention which are not required to be essentially free of sulfate ions,the polyoxoanion may be prepared by the methods which add sulfuric acidin the aqueous solution, U.S. Pat. No. 4,146,574, incorporated byreference entirely, teaches a method for the preparation of solutionsconsisting of free phosphomolybdovanadic acids.

Alternatively, the present invention provides a process for the directpreparation of acidic aqueous solutions of salts of polyoxoacidscomprising vanadium without the introduction of mineral acids other thanthe polyoxoacid or its component oxoacids. The acidity of the resultingsolutions is readily adjusted by the balance of salt cations and protonsin the salt.

Process for the Preparation of Polyoxoanion Solutions:

According to the present invention, acidic aqueous solutions of salts ofpolyoxoanions comprising vanadium are prepared by dissolving in wateroxides, oxoacids, and/or salts of oxoanions of the componentpolyoxoanion elements, and optionally salts of carbonate, bicarbonate,hydroxide, and oxide, such that the resulting ratio of protons and saltcountercations balancing the net negative charge of the resultingpolyoxanions in the solution provides a hydrogen ion concentration insolution greater than 10⁻⁵ moles/liter.

Preferably, the resulting hydrogen ion concentration is greater than 10⁻³ moles/liter, and most preferably, greater than 0.1 moles/liter.

Preferred Keggin phosphomolybdovanadate salts are preferably prepared insolution by dissolving vanadium oxide and/or vanadate salt, molybdenumoxide and/or molybdate salt, phosphoric acid and/or phosphate salt, andoptionally carbonate, bicarbonate, and/or hydroxide salt in water, suchthat the ratio of protons (3+n-p) and other salt countercations (p)balancing the negative charge of the phosphomolybdovanadates (3+n) inthe solution provides the desired hydrogen ion concentration in thesolution. Preferably the vanadium, molybdenum, and phosphorus reactantsare added in ratios corresponding to the desired average Keggincomposition of the solution.

The temperature of the preparation process may be within the range 50 to120° C. It is most conveniently operated in boiling water at about 100°C.

Typically, a solution of alkali vanadate, for example sodiummetavanadate (NaVO₃) or hexasodium decavanadate (Na₆ V₁₀ O₂₈), isprepared in water. This solution can be prepared by dissolving solidsalts into water, but is prepared most economically by adding alkalicarbonate (e.g. Na₂ CO₃), alkali bicarbonate (e.g. NaHCO₃), or alkalihydroxide (e.g. NaOH) to a suspension of vanadium oxide (V₂ O₅) in waterand heating to complete the reactive dissolution. Then, molybdenum oxideand phosphoric acid (or alkali phosphate salt) are added to the alkalivanadate solution and heating is continued to complete the preparationof an acidic aqueous phosphomolybdovanadate salt solution. Finally, thesolution is adjusted to the desired concentration by evaporation and/orvolumetric dilution.

Additional basic alkali salt (carbonate, bicarbonate, of hydroxide) canbe added at any point during or after the preparation to furtherneutralize the resulting polyoxoacid solution and obtain decreasedacidity; that is, to adjust the value p in the designation {A_(p)H.sub.(3+n-p) PMo.sub.(12-n) V_(n) O₄₀ }.

When solutions having the same phosphorus concentration and vanadiumcontent, n, but different acidities (different p) are already preparedand available, solutions of intermediate acidity (intermediate p) can beprepared by blending the available solutions in the appropriatevolumetric ratios. More generally, solutions of determinate compositioncan be prepared by blending measured volumes of two or more solutions,of known phosphorus concentration, vanadium content (n), and salt cationcontent (p).

Hydrogen Ions:

Hydrogen ions and hydrogen ion concentrations, as used herein, havetheir usual meaning. Hydrogen ions in aqueous solution are free, aquatedprotons. Hydrogen ion concentration is not meant to include protonsbound in other solute species, such as in partially protonatedpolyoxoanions or bisulfate.

Hydrogen ions may be provided by providing an acid which dissociatesprotons when dissolved in aqueous solution. Organic and mineral acidswhich are sufficiently acidic to provide the desired hydrogen ionconcentration are suitable. The acid is preferably inert to oxidationand oxidative destruction under intended process conditions. Acidanhydrides and other materials which hydrolytically release protons onreaction with water may likewise be used to provide hydrogen ions.

Strong mineral acids, such as polyoxoacids, sulfuric acid, hydrochloricacid, and the like, are preferred sources of hydrogen ions. Particularlypreferred are polyoxoacids. Certain solutions and related processes ofthe present invention are essentially free of sulfuric acid. Certainsolutions and related processes of the present invention are essentiallyfree of mineral acids other than of polyoxoacids and hydrohalic acids.

Hydrogen ion concentrations of polyoxoanion solutions, as recitedherein, refer to the hydrogen ion concentration when essentially all thepolyoxoanion is in its fully oxidized state, which is when essentiallyall the vanadium in the polyoxoanion solution is in the vanadium(V)state. It has been determined that the acidity of the preferredpolyoxoanion solutions change with reduction, and these changes are notyet completely understood and predictable. (For example, 0.30M {Na₃ H₃PMo₉ V₃ O₄₀ } solution has a hydrogen ion concentration greater than0.10 moles/liter in equilibrated fully oxidized state, but less than0.01 moles/liter in equilibrated fully reduced state, when all thevanadium is in the vanadium(V) state.) The preferred polyoxoanions ofthe present invention are most readily prepared essentially fullyoxidized, and can be readily returned to that condition by reaction withdioxygen according to processes of the present invention. In the contextof determining hydrogen ion concentrations, the phrase "when essentiallyall the oxidant is in its oxidized state" means when the solution ofoxidant is sufficiently oxidized so as to have the hydrogen ionconcentration which is obtained when it is fully oxidized.

The hydrogen ion concentration is sufficient to provide an acidicsolution having a hydrogen ion concentration greater than 10⁻⁵mole/liter. Preferably, the hydrogen ion concentration is greater than10⁻³ mole/liter, and most preferably, greater than 0.1 moles/liter.Certain solutions and related processes of the present inventionspecifically comprise hydrogen ions at a concentration greater than 0.1mole per liter of solution when essentially all the oxidant is in itsoxidized state.

Hydrogen Ion Concentration Measurement:

Background references for polyoxoanion solutions generally recite "pH"values for the solution but do not specify methods for determining them.pH is technically defined as -log[α_(H+) ], where α_(H+) is the hydrogenion activity. The hydrogen ion activity is identical to the hydrogen ionconcentration in otherwise pure water. The hydrogen ion activity andhydrogen ion concentration are still good approximations of each otherin aqueous solutions which are low in ionic strength and otherwiseapproximately ideal. Solutions of polyoxoacids at decimolarconcentrations, typical in background references and in the presentinvention, have high ionic strength and are very non-ideal solutions,especially when they also contain high concentrations of other mineralacid salts.

The common method to obtain pH measurements of aqueous solutions usespH-sensitive glass electrodes, monitored with an electrometer (a "pHmeter"). Such electrodes are known to exhibit an "acid error", measuringincreasingly incorrect "pH"s as pH is decreased below 2 and especiallyat real pH 1 and below. Moreover, successful measurement at any pH levelrequires calibration with solutions of similar ionic media and ionicstrength. Common calibration solutions for pH meters are at relativelylow ionic strength and of very different ionic media compared todecimolar polyoxoanion salt solutions. We have found that usingdifferent common calibration solutions can lead to different "pH"measurements for the same polyoxoanion solution. Unless a disclosurecontains a recitation of the method of "pH" measurement for thesesolutions, including the methods of calibration, one having ordinaryskill does not know what a reported "pH" value really means, nor how toreproduce it.

We have developed a more definitive method of measuring hydrogen ionconcentration in the polyoxoanion solutions of the present invention. ItIs based on the observation (by ³¹ P- and ⁵¹ V-NMR studies) that insolutions designated {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ }, PMo₁₁ VO₄₀ ⁴⁻ isessentially the only species present. It was further determined thatPMo₁₁ VO₄₀ ⁴⁻ remains completely unprotonated even in concentratedsolutions (>0.3M) of the free acid {H₄ PMo₁₁ VO₄₀ }. (Species having twoor more vanadia do become protonated in acidic aqueous solutions.)Accordingly, for solutions of {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ }, thehydrogen ion concentration is the phosphorus concentration multiplied by(4-p). Such solutions were prepared and used to calibrate glass pHelectrodes for measurement of the hydrogen ion concentration ofsolutions of undetermined acidity, having the same phosphorusconcentration. This method is illustrated in the examples.

Sulfate ions:

Sulfate ions, as used herein, is meant to include both sulfate dianion(SO₄ =) and bisulfate anion (HSO₄ -). Since sulfuric acid is a verystrong acid, addition of sulfuric acid to an aqueous solution results ina solution of sulfate and/or bisulfate ions, depending on the acidity ofthe solution.

Certain solutions and related processes of the present invention are"essentially free of sulfate ions". This means the concentration ofsulfate and/or bisulfate salts is sufficiently low so that theirundesired influence on palladium catalyst activity, palladium catalyststability, volumetric olefin oxidation rate, or volumetric dioxygenreaction rate is not significantly manifested. This can be readilydetermined experimentally. Preferably, these solutions are free ofsulfate and/or bisulfate salts.

Chloride ions:

Chloride ions can be provided by any chloride-containing compound whichreadily dissolves in water, or reacts with water, to release free,aquated chloride ions into solution. Suitable chloride-containingcompounds include hydrochloric acid, chlorides and oxychlorides ofoxoanion-forming elements, chloride complexes and chloride salts, andthe like. Examples of chlorides and oxychlorides of the oxoanion-formingelements are PCl₅, POCl₃, VOCl₃, VOCl₂, MoOCl₄, and the like. Suitablechloride salt countercations are those which are inert, or in some wayadvantageous (for example, Pd^(II)), under the reaction conditions andwhich do not precipitate insoluble polyoxoanion salts out of aqueoussolution. Preferred chloride-containing compounds are hydrochloric acid,palladium chloride compounds, and chloride salts of alkali metal cationsand alkaline earth cations which do not precipitate insolublepolyoxoanion salts. Examples of suitable palladium chloride compoundsare PdCl₂, Na₂ PdCl₄, K₂ PdCl₄, and the like. Examples of suitablealkali and alkaline earth salts are lithium chloride (LiCl), sodiumchloride (NaCl), potassium chloride (KCl), and magnesium chloride(MgCl₂).

Significant amounts of chloride may also be present as impurities in thestarting materials for polyoxoanion preparation. For example, wesurprisingly discovered that several commercial sources of sodiumvanadate are sufficiently contaminated with chloride to provideeffective amounts of chloride in polyoxoanion solutions prepared fromthem.

Certain solutions and related processes of the present inventioncomprise chloride at concentrations greater than coincidental to usingPdCl₂ as the palladium source; that is greater than twice the palladiumconcentration. Preferably, the chloride concentration is greater thanfour times the palladium concentration. Most preferably, the chlorideconcentration is at least 5 millimolar. There is no particular upperlimit on the chloride concentration, but is preferably less than aconcentration at which the palladium catalyst activity becomes inverselydependent on the square of the chloride concentration. Chloride isusually present at a concentration of 0.001 to 1.0 moles/liter,preferably 0.005 to 0.50 moles per liter, and most preferably 0.010 to0.100 moles per liter. Typically, the chloride is present in millimolarto centimolar concentrations, where unquantified "millimolarconcentrations" refers to concentrations of 1.0 to 10.0 millimolar, andunquantified "centimolar concentrations" refers to concentrations of10.0 to 100.0 millimolar. Generally, the chloride is present in thesesolutions at a molar ratio of 10/1 to 10,000/1 relative to palladium.

Chloride may also be provided by copper chlorides, for example byresidual Wacker catalyst retained in an industrial plant designed tooperate the Wacker process chemistry after draining the Wacker catalystsolution. However, the chloride-containing solutions and relatedprocesses of the present invention are preferably essentially free ofcopper ions. "Essentially free of copper ions ions" means the olefinoxidation process with the solution does not produce substantiallyhigher amounts of chlorinated organic by-products than a correspondingsolution which is free of copper ions.

Process Conditions:

Broadly, olefin oxidation processes of the present reaction areconducted under oxidative conditions sufficient to oxidize the olefin toa carbonyl product. Likewise, in processes involving reaction ofdioxygen, the dioxygen reaction is conducted under oxidative conditionssufficient to utilize dioxygen to oxidize the olefin, or intermediately,to regenerate the polyoxoanion oxidant in its oxidized state.

The preferred temperature range for processes of the present inventionvaries with the identity of the olefin and is interdependent with suchfactors as the olefin concentration in aqueous solution, chloride ionconcentration, palladium concentration, and other factors whichdetermine reaction rates. Increasing temperature generally providesincreased reaction rates, although these increases are slight forreactions which are limited by diffusion. In some cases, lowertemperatures may be preferred to avoid troublesome side-reactions. Intwo-stage operation, temperatures for the olefin reaction and thedioxygen reaction can be set independently. Generally, temperaturesutilized in processes of the present invention may range from about 20°to about 200° C., usually in the range 60° to 160° C. For gaseousolefins, such as ethylene, propylene, and butenes, the temperature ispreferably in the range 90° to 130° C.

Pressures for the processes of the present invention depend strongly onthe nature of the olefin, whether gaseous or liquid under the reactionconditions, whether dioxygen reaction is conducted simultaneously orseparately with the olefin oxidation reaction, whether oxygen is addedas oxygen or air, and reaction temperatures. For example, at reactiontemperatures less than 100° C., the atmospheric boiling point of water,with olefins which are liquid under the reaction conditions, in theabsence of dioxygen, the olefin oxidation process may be convenientlyconducted at atmospheric pressure. For temperatures near or above 100°C. and above, water vapor contributes significantly to the totalpressure in the reactor device.

For gaseous olefins, elevated partial pressure is usually utilized toincrease the concentration of olefin in the gas phase in contact withthe liquid phase and thereby increase its solubility in the liquidphase, to increase reaction rates and decrease reactor volumes.Generally, gaseous olefins are reacted at partial pressures of 1atmosphere to 100 atmospheres, typically in the range 4 atmospheres(about 60 psi) to 20 atmospheres (about 300 psi). In two-stage mode,gaseous olefins are preferably reacted at partial pressures in the rangeof 8 atmospheres (about 120 psi) to 12 atmospheres (about 180 psi).

In certain solutions and processes of the present invention, olefin isdissolved in the catalyst solution at concentrations effective for itsrate of oxidation to be at least 1 (millimole olefin/litersolution)/second, or at concentrations effective to provide a palladiumturnover frequency of at least 1 (mole olefin, mole palladium)/second,or preferably both. Reaction conditions and mixing conditions which meetthese criteria can be established by routine experimentation, forexample using the procedures of the following Examples. In certainsolutions and processes of the present invention, the olefin isdissolved at concentrations such that its rate of oxidation is notfurther increased by further increasing its concentration (olefinsaturation kinetics).

For dioxygen reaction processes, elevated partial pressure is usuallyutilized to increase the concentration of oxygen in the gas phase incontact with the liquid phase, to increase reaction rates and decreasereactor volumes. Generally, oxygen is reacted at partial pressures of0.2 atmosphere (1 atmosphere air) to 100 atmospheres, typically in therange 0.2 atmospheres to 20 atmospheres, and preferably in the range 1atmosphere (about 15 psi) to 10 atmosphere (about 150 psi).

For oxidation of gaseous olefins by dioxygen in two stage mode, thetotal pressures in the olefin reactor and the dioxygen reactor aretypically similar, but may be varied independently. In two stage mode,compressed air is typically used, but oxygen could be used as well.

For oxidation of gaseous olefins by dioxygen in one-stage mode, oxygenis typically used and olefin and oxygen are typically fed in nearstoichiometric ratios, about 2:1.

Liquid olefins can be reacted neat or in combination with substantiallyinert diluents. Generally, the concentration of the liquid olefin in asecond liquid olefinic phase is increased to increase reaction rates anddecrease reactor volumes. However, in some applications, it may beadvantageous to use a diluent. Such diluent may improve the mixing andmass transfer of the olefin into the aqueous catalyst solution, orprovide improved recovery of the carbonyl product by improvedliquid-liquid phase distribution, and/or improved phase separation. Inother applications, the olefinic feed may be obtained in combinationwith substantially inert diluents which are more easily or economicallyseparated from the carbonyl product than from the olefin. For example,butenes may be obtained in combination with butane, cyclohexene may beobtained in combination with cyclohexane and/or benzene. In otherapplications, it may be desirable to use a cosolvent diluent whichmiscibilizes the olefinic and aqueous solution components.

Suitable reactors for the processes of the invention provide forefficient mixing of olefinic and aqueous catalyst phases. Efficientmixing in the olefin reaction is established when the rate of thereaction is governed by the chemical kinetics of catalysis, and is notlimited by diffusion of the olefin into the aqueous phase. Once thatcondition is established, dissolved olefin concentration in the aqueoussolution can be increased by increasing the olefin concentration in theolefinic phase (for gaseous olefins, by increasing the partial pressureof the olefin). In some embodiments, the olefin concentration in theaqueous solution is effective for the olefin oxidation rate to becomeindependent of the olefin concentration in the aqueous solution (olefinsaturation kinetics). Efficient mixing in the dioxygen reaction isestablished when the diffusion-limited dioxygen reaction rate proceedsrapidly enough for convenient and economical utilization in the intendedapplication, preferably at least 1 (millimole dioxygen/litersolution)/second.

Reactors and associated equipment in contact with the aqueous catalystsolution should withstand the oxidizing nature of the solution andprocesses without corrosion. For solutions and processes in the absenceof chloride, stainless steel, Hastelloy C, glass, and titanium providesuitable equipment surfaces. For solutions and processes in the presenceof chloride, titanium and/or glass is preferred.

The carbonyl product of the reaction may be separated from the reactionsolution by usual methods such as vaporizing ("flashing" by pressuredrop), stripping, distilling, phase separation, extraction, and thelike. It is preferred that the carbonyl product is recovered whileleaving the aqueous solution in a form suitable to use directly incontinued process operation. In two-stage operation, it is preferred toremove the product before the dioxygen reaction. In one-stage operationfor a volatile carbonyl product, it is preferred to continuously removethe product as it is formed in the process.

Processes for the oxidation of palladium (0) to palladium (II) requireonly that the palladium (0) is contacted with the polyoxoanion oxidantsolution under conditions sufficient to oxidize palladium (0) topalladium (II) at the desired rate. Temperature, chloride ionconcentration, and palladium (0) surface area are particularlyinterdependent in determining such conditions. Generally, the greaterthe chloride ion concentrations, the lower the temperature required toachieve a desired rate. If the dissolved palladium (II) is to be used inan olefin oxidation process, the conditions are generally similar tothose of the olefin oxidation process.

Solutions and Processes wherein the hydrogen ion concentration isgreater than 0.1 mole/liter:

Solutions and related processes of the present invention wherein thehydrogen ion concentration is greater than 0.1 mole/liter need not beessentially free of sulfate, nor further comprise chloride ions, norfurther comprise any minimum dissolved olefin concentration. However,preferred embodiments of such solutions and processes may include one ormore of these features.

Solutions and Processes essentially free of sulfate:

Solutions and related processes of the present invention which areessentially free of sulfate ions need not also comprise a hydrogen ionconcentration greater than 0.1 mole/liter, nor further comprise chlorideions, nor further comprise any minimum dissolved olefin concentration.However, preferred embodiments of such solutions and processes mayinclude one or more of these features. In particular, it is preferredthat the hydrogen ion concentration of the solution be at least greaterthan 10⁻³ moles/liter.

Solutions and Processes comprising Chloride:

Solutions and related processes of the present invention using thosesolutions which comprise chloride ions need not also comprise a hydrogenion concentration greater than 0.1 mole/liter, nor also be essentiallyfree of sulfate, nor further comprise any minimum dissolved olefinconcentration. However, preferred embodiments of such solutions andprocesses may use one or more of these features. In particular, it ispreferred that the hydrogen ion concentration of the solution be atleast greater than 10⁻³ moles/liter.

It is especially preferred that solutions and processes which do notprovide effective concentrations of dissolved olefin, do comprisechloride ions.

Solutions and Processes comprising dissolved olefin at effectiveconcentrations:

Solutions and related processes of the present invention which comprisecertain effective dissolved olefin concentrations in the aqueouscatalyst solution, and processes which comprise certain effective mixingconditions need not also comprise a hydrogen ion concentration greaterthan 0.1 mole/liter, nor be essentially free of sulfate, nor furthercomprise chloride ions. However, preferred embodiments of such solutionsand processes include one or more of these features. In particular, itis preferred that the hydrogen ion concentration of the solution be atleast greater than 10⁻³ moles/liter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overlay plot of ethylene consumptions vs. time in palladiumcatalyzed ethylene oxidations by 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } solutionscontaining various concentrations of chloride ions. The plottedreactions are further described at Examples 25, 32, and 34 (Table 2).

FIG. 2 is a scatter plot, on logarithmic axes, of initial palladiumturnover frequencies vs. chloride ion concentrations for palladiumcatalyzed ethylene oxidations by 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } solutionscontaining various concentrations of chloride ions. The plotted datacorrespond to Example 24-42, as listed in Table 2.

FIG. 3 is a scatter plot of measured palladium catalyst turnoverfrequencies vs. -log[H⁺ ] (the negative base 10 logarithm of thehydrogen ion concentration in moles per liter) for palladium catalyzedethylene oxidations by 0.30M {Na_(p) H.sub.(5-p) PMo₁₀ V₂ O₄₀ }solutions containing various concentrations of chloride ions. Theplotted data correspond to Examples 44-61, listed in Table 3.

FIG. 4 is an overlay plot of ethylene consumptions vs. time in palladiumcatalyzed ethylene oxidations by 0.30M {Na_(p) H.sub.(6-p) PMo₉ V₃ O₄₀ }solutions having various hydrogen ion concentrations (various p) and 25millimolar chloride ion concentration. The plotted reactions are furtherdescribed at Examples 62, 64, and 65 (Table 4).

EXAMPLES

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following specific examples are, therefore,intended to be merely illustrative, and not limitative of the disclosurein any way whatsoever. Further exemplification is provided in co-filedU.S. patent applications Ser. Nos. 07/689,050, 07/689,048, and07/675,937, each of which is incorporated by reference entirely.

Every -log[H⁺ ] value recited in these examples and in the drawings isthe base 10 logarithm of the hydrogen ion concentration in units ofmole/liter. Thus, -log[H⁺ ]=1.0 corresponds to a hydrogen ionconcentration of 0.10 mole/liter, and a -log[H⁺ ]<1.0 corresponds to ahydrogen ion concentration greater than 0.10 mole/liter

Preparations of Polyoxoanion Solutions:

Examples 1 through 8 and 10 through 22 show preparations of solutions ofpolyoxoanions within the scope of the invention which are useful in theinventive catalyst solutions and processes. Except when otherwisestated, the exemplified polyoxoanion syntheses used H₃ PO₄ (food grade),MoO₃ (pure molybdic oxide), and V₂ O₅ (chemical grade) and wereconducted in a 3 neck Morton flask, of 5.0 liter or 12.0 liter capacity,equipped with an electric heating mantle, an efficient refluxcondenser/demister, a powder addition funnel and a high torque overheadmechanical stirrer. Distilled water rinses were used for every solutiontransfer in the preparations to ensure essentially quantitative recoveryof dissolved solution components in the final solution.

EXAMPLE 1

Preparation of 0.30M {H₄ PMo₁₁ VO₄₀ }: An aqueous solution of thephosphomolybdovanadic free acid H₄ PMo₁₁ VO₄₀ was prepared according tothe following reaction equation:

    0.5 V.sub.2 O.sub.5 +11 MoO.sub.3 +H.sub.3 PO.sub.4 +0.5 V.sub.2 O→H.sub.4 PMo.sub.11 VO.sub.40 (aq)

45.47 grams granular V₂ O₅ (0.25 mole) and 791.67 grams MoO₃ (5.50 mole)were suspended in 5.0 liters distilled water with moderate stirring.57.37 grams 85.4% (w/w) H₃ PO₄ (0.05 mole) was added, the mixture wasdiluted to a total volume of 10.0 liters with an additional 4.5 litersof distilled water, and the mixture was heated to reflux. After 2 daysat reflux, 15 drops of 30% H₂ O₂ was added dropwise to the mixture. Themixture was maintained at reflux for a total of 7 days, giving aslightly turbid light burgundy-red mixture. The mixture was cooled toroom temperature and clarified by vacuum filtration. The volume of thesolution was reduced to about 1.5 liters by rotating-film evaporation at50° C. under vacuum. The resulting homogenous, clear, burgundy-redsolution was volumetrically diluted with distilled water to a totalvolume of 1.667 liters, giving 0.30 molar H₄ PMo₁₁ VO₄₀.

H₄ PMo₁₁ VO₄₀ is a very strong acid whose four acidic hydrogens arecompletely dissociated from the polyoxoanion as hydrogen ions in thissolution. The hydrogen ion concentration of this solution is explicitly1.2 mole/liter; -log[H⁺ ]=-0.08

EXAMPLE 2

Preparation of 0.30M {Na₄ PMo₁₁ VO₄₀ }: An aqueous solution of thephosphomolybdovanadate full salt Na₄ PMo₁₁ VO₄₀ was prepared accordingto the following reaction equations:

    0.5 V.sub.2 O.sub.5 +0.5 Na.sub.2 CO.sub.3 →NaVO.sub.3 (aq)+0.5 CO.sub.2 ↑1.5 Na.sub.2 CO.sub.3 +NaVO.sub.3 (aq)+11 MoO.sub.3 +H.sub.3 PO.sub.4 →Na.sub.4 PMo.sub.11 VO.sub.40 +1.5 CO.sub.2 ↑+32 H.sub.2 O

109.13 grams granular V₂ O₅ (0.60 mole) was suspended in 1.0 literdistilled water in a Morton flask with overhead stirring. The mixturewas heated to ca. 60° C. and 63.59 grams, granular Na₂ CO₃ (0.60 mole)was slowly added in portions to the rapidly stirred suspension, causingCO₂ liberation and dissolution of the V₂ O₅ to give an essentiallyhomogeneous solution. The solution was heated at reflux for 60 minutes.Approximately 1 ml of 30% H₂ O₂ was added dropwise to the mixture, whichwas maintained at reflux for an additional 60 minutes, then cooled toroom temperature. The solution was clarified by vacuum filtration, andthe resulting clear, orange sodium vanadate solution was then returnedto a Morton flask with additional distilled water. 1900.01 grams MoO₃(13.2 mole) was added with rapid stirring, the mixture was heated toabout 60° C., and 190.78 grams granular Na₂ CO₃ (1.80 mole) was slowlyadded in portions to the rapidly stirred suspension, causing CO₂liberation and dissolution of MoO₃. 137.70 grams 85.4% (w/w) H₃ PO₄(1.20 mole) was then slowly added to the mixture, and the mixture washeated at the reflux and thereby converted to a clear, dark,burgundy-brown solution. After 3 hours at reflux, the homogenoussolution was cooled to room temperature and volumetrically diluted withdistilled water to a total volume of 4.0 liters, giving 0.30 molar {Na₄PMo₁₁ VO₄₀ }.

EXAMPLE 3

Preparation of 0.30M {Li₄ PMo₁₁ VO₄₀ }: The procedure was the same asfor {Na₄ PMo₁₁ VO₄₀ } in Example 2 except that 133.00 grams granular Li₂CO₃ (1.80 mole) was substituted for the Na₂ CO₃.

These solutions of 0.30M {A₄ PMo₁₁ VO₄₀ }, A=Na, Li, were found to bereproducibly slightly acidic, having hydrogen ion concentrations˜0.001M. Presumably, a minute fraction of the Keggin polyoxoanion ishydrolytically dissociated, with release of hydrogen ions from water, atequilibrium. 162 MHz ³¹ P-NMR and 105 MHz ⁵¹ V- NMR spectra of thesesolutions were essentially identical to those of 0.30M {H₄ PMo₁₁ VO₄₀ },showing substantially only the PMo₁₁ VO₄₀ ⁴⁻ ion.

EXAMPLES 4-8

Preparations of 0.30M {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ }, A=Na, Li; Thefollowing 0.30M {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ } solutions were preparedby blending 0.30M {H₄ PMo₁₁ VO₄₀ } (Example 1) and 0.30M {A₄ PMo₁₁ VO₄₀}, A=Na (Example 2) or Li (Example 3) in (4-p):p volumetric ratios. Thehydrogen ion concentration in each of these solutions is explicitly 0.30(4-p) mole/liter, as indicated:

    ______________________________________                                        Example 4:                                                                            0.30M {Na.sub.0.67 H.sub.3.33 PMo.sub.11 VO.sub.40 }                                              -log[H+] = 0.00                                   Example 5:                                                                            0.30M {Na.sub.3.67 H.sub.0.33 PMo.sub.11 VO.sub.40 }                                              -log[H+] = 1.00                                   Example 6:                                                                            0.30M {Li.sub.0.67 H.sub.3.33 PMo.sub.11 VO.sub.40 }                                              -log[H+] = 0.00                                   Example 7:                                                                            0.30M {Li.sub.3.67 H.sub.0.33 PMo.sub.11 VO.sub.40 }                                              -log[H+] = 1.00                                   Example 8:                                                                            0.30M {Li.sub.2.67 H.sub.1.33 PMo.sub.11 VO.sub.40 }                                              -log[H+] = 0.40                                   ______________________________________                                    

Each of these solutions is alternatively prepared by adding theappropriate amount of the alkali (Na, Li) carbonate, bicarbonate orhydroxide to the {H₄ PMo₁₁ VO₄₀ } solution or to a {A_(p) H.sub.(4-p)PMo₁₁ VO₄₀ } solution of lesser p.

The following Example shows a method for measurement of the hydrogen ionconcentration in acidic aqueous polyoxoanion solutions and correspondingcatalyst solutions, which is particularly preferred for determininghydrogen ion concentrations in such solutions having hydrogen ionconcentrations greater than 0.10 mole/liter. The described procedureswere used to determine all of the hydrogen ion concentrations recited inthe present examples and in the drawings, usually expressed as -log[H⁺]. These recited hydrogen ion concentrations were measured with theindicated polyoxoanions in solution in their oxidized state.

EXAMPLE 9

Measurement of Hydrogen Ion Concentration: -log[H⁺ ] measurements weremade with a commercial glass combination pH electrode ((Orion) RossCombination pH electrode) and commercial digital-display pHpotentiometer (Corning, Model 103, portable pH meter). In pH displaymode, the potentiometer was calibrated to display 1.00 with theelectrode in 0.30M {Na₃.67 H₀.33 PMo₁₁ VO₄₀ } (Example 5) and 0.00 in0.30M {Na₀.67 H₃.33 PMo₁₁ VO₄₀ } (Example 4), without intermediateadjustment. This calibration was used to measure -log[H⁺ ] in 0.30M{Na_(p) H.sub.(3+n-p) PMo.sub.(12-n) V_(n) O₄₀ } solutions with p≧0having -log[H⁺ ]≦1.00.

To measure -log[H⁺ ] in 0.30M {aNa_(p) H.sub.(3+n-p) PMo.sub.(12-n)V_(n) O₄₀ } solutions having -log[H⁺ ]>1.00, the potentiometer wasinstead calibrated with the 0.30M {Na₃.67 H₀.33 PMo₁₁ V₁ O₄₀ } solution,-log[H⁺ ]=1.00, and 0.10M Na₁.6 H₁.6 H₁.4 PO₄ pH 7.0 buffer (preparedfrom Na₂ HPO₄ ·7H₂ O and NaH₂ PO₄ ·H₂ O in distilled water), taken to be-log[H⁺ ]=7.0. (pH 7 is far from the hydrogen ion concentrations in theso measured polyoxoanion solutions, so that any discrepancy between pHand -log[H⁺ ] in this calibration solution only insignificantly effectsthe accuracy of those measurements.)

To measure -log[H⁺ ] in 0.30M {Li_(p) H.sub.(3+n-p) PMo.sub.(12-n) V_(n)O₄₀ } solutions with p>0, the corresponding Li⁺ calibration solutionswere used: 0.30M {Li₀.67 H₃.33 PMo₁₁ VO₄₀ }, -log[H⁺ ]=0.00 (Example 6);0.30M {Li₃.67 H₀.33 PMo₁₁ VO₄₀ }, -log[H⁺ ]=1.00 (Example 7); and 0.10MLi₁.6 H₁.4 PO₄ (prepared from H₃ PO₄ and LiOH in distilled water), takento be -log[H⁺ ]=7. By this calibration, 0.30M {Li₂.67 H₁.33 PMo₁₁ VO₄₀ }(Example 8), with known -log[H⁺ ]=0.40, was measured to be -log[H⁺]=0.37, indicating the accuracy of the measurement.

To measure -log[H⁺ ] in solutions having other Keggin polyoxoanionconcentrations, calibration solutions of {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ }at the same other polyoxoanion concentration are used: -log[H⁺ ] for X M{A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ } is X(4-p).

Although hydrogen ion concentrations were quantitatively measured forthe polyoxoanion and catalyst solutions in the present Examples, it isoften sufficient to simply discriminate qualitatively whether thehydrogen ion concentration is greater than or less than 0.10 mole/liter.A single calibration solution of {A_(p) H.sub.(4-p) PMo₁₁ VO₄₀ } with ahydrogen ion concentration of 0.10 mole/liter can be used to determineif another polyoxoanion solution has a hydrogen ion concentrationgreater than or less than 1.10 mole/liter by comparison. Preferably, thecalibration solution has the same polyoxoanion concentration and thesame salt countercation as the other solution in question. Any physicalmeasurement technique capable of discriminating between solutions havinghydrogen ion concentrations greater than or less such a singlecalibration solution is suitable for making the comparison.

Example 10

Preparation of 0.30M{Na₂ H₃ PMo₁₀ V₂ O₄₀ }: An aqueousphosphomolybdovanadic acid partial salt solution designated 0.30M {Na₂H₃ PMo₁₀ V₂ O₄₀ } was prepared according to the following reactionequations:

    V.sub.2 O.sub.5 +Na.sub.2 CO.sub.3 →2NaVO.sub.3 (aq)+CO.sub.2 ↑2NaVO.sub.3 (aq)+10MoO.sub.3 +H.sub.3 PO.sub.4 →Na.sub.2 H.sub.3 PMo.sub.10 V.sub.2 O.sub.40 (aq)

218.26 grams granular V₂ O₅ (1.20 mole) was suspended in 2.0 litersdistilled water in a Morton flask with overhead stirring and the mixturewas heated to about 60° C. 127.19 grams granular Na₂ CO₃ (1.20 mole) wasslowly added in portion to the rapidly stirred mixture, causing CO₂liberation and dissolution of the V₂ O₅ to give and essentiallyhomogeneous solution. The solution was heated at the reflux for 60minutes. The solution was then lime green color due to dissolved V^(IV)which was originally present in the V₂ O₅. Approximately 1 ml of 30% H₂O₂ was added dropwise to the mixture causing the dark, black-blue greencolor to fade, leaving a slightly turbid, pale-tan sodium vanadatesolution. The solution was maintained at reflux for an additional 60minutes to ensure the decomposition of excess peroxide and then cooledto room temperature. The solution was clarified by vacuum filtration toremove the small amount (>0.1 grams) of brown solid which containedalmost all the iron and silica impurities originally present in the V₂O₅. The clear, orange sodium vanadate solution was then returned to aMorton flask, and 1727.28 grams MoO₃ (12.00 mole) was added with rapidoverhead stirring. The mixture was heated to about 60° C. and 137.7grams 85.4% (w/w) H₃ PO₄ (1.20 mole) was added. The mixture was heatedat the reflux and thereby converted to a clear, dark, burgundy-redsolution. After 3 hours at reflux, the homogenous burgundy-red solutionwas cooled to room temperature and volumetrically diluted with distilledwater to a total volume of 4.00 liters, giving 0.30M{Na₂ H₃ PMo₁₀ V₂ O₄₀}.

The hydrogen ion concentration of 0.30M {Na₂ H₃ PMo₁₀ V₂ O₄₀ } wasmeasured to be 0.67 mole/liter; -log[H⁺ ]=0.18.

EXAMPLE 11

Preparation of 0.30M {Na₅ PMo₁₀ V₂ O₄₀ }: An aqueousphosphomolybdovanadate full salt solution designated 0.30M {Na₅ PMo₁₀ V₂O₄₀ } was prepared according to the following reaction equations:

    V.sub.2 O.sub.5 +Na.sub.2 CO.sub.3 →2NaVO.sub.3 (aq)+CO.sub.2 ↑1.5Na.sub.2 CO.sub.3 +2NaVO.sub.3 (aq)+10MoO.sub.3 +H.sub.3 PO.sub.4 →Na.sub.5 PMo.sub.10 V.sub.2 O.sub.40 +1.5CO.sub.2 ↑+1.5H.sub.2 O

The procedure was the same as in Example 10 except that after theaddition of the MoO₃, the mixture was heated to the reflux and anadditional 190.78 grams granular Na₂ CO₃ (1.80 mole) was slowly added inportions to the stirred suspension, causing CO₂ liberation, before theaddition of the H₃ PO₄.

EXAMPLES 12-16

Preparations of 0.30M {Na_(p) H.sub.(5-p) PMo₁₀ V₂ O₄₀ } solutions: Thefollowing polyoxoacid partial salt solutions designated 0.30M {Na_(p)H.sub.(5-p) PMo₁₀ V₂ O₄₀ } were prepared by blending 0.30M {Na₂ H₃ PMo₁₀V₂ O₄₀ } (Example 10) and 0.30M {Na₅ PMo₁₀ V₂ O₄₀ } (Example 11) in(5-p):(p-2) volumetric ratios, and their hydrogen ion concentrationswere measured as indicated:

    ______________________________________                                        Example 12                                                                            0.30M {Na.sub.4 HPMo.sub.10 V.sub.2 O.sub.40 }                                                    -log[H+] = 0.69                                   Example 13                                                                            0.30M {Na.sub.4.40 H.sub.0.60 PMo.sub.10 V.sub.2 O.sub.40                                         -log[H+] = 0.91                                   Example 14                                                                            0.30M {Na.sub.4.47 H.sub.0.53 PMo.sub.10 V.sub.2 O.sub.40                                         -log[H+] = 1.00                                   Example 15                                                                            0.30M {Na.sub.4.80 H.sub.0.20 PMo.sub.10 V.sub.2 O.sub.40                                         -log[H+] = 1.43                                   Example 16                                                                            0.30M {Na.sub.4.94 H.sub.0.06 PMo.sub.10 V.sub.2 O.sub.40                                         -log[H+] = 1.96                                   ______________________________________                                    

Each of these solutions is alternatively prepared by adding theappropriate amount of the sodium carbonate, bicarbonate or hydroxide toa 0.30M {Na_(p) H.sub.(5-p) PMo₁₀ V₂ O₄₀ } solution of lesser p.

EXAMPLE 17

Preparation of 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ }: The phosphomolybdovanadicpartial salt solution designated {Na₃ H₃ PMo₉ V₃ O₄₀ } was preparedaccording to the following reaction equations:

    1.5V.sub.2 O.sub.5 +1.5Na.sub.2 CO.sub.3 →3NaVO.sub.3 (aq)+1.5CO.sub.2 ↑3NaVO.sub.3 (aq)+9 MoO.sub.3 +H.sub.3 PO.sub.4 →Na.sub.3 H.sub.3 PMo.sub.9 V.sub.3 O.sub.40 (aq)

818.46 grams granular V₂ O₅ (4.50 moles) was suspended in 3.5 litersdistilled water in a Morton flask with overhead stirring and the mixturewas heated to about 60° C. 476.95 grams granular Na₂ CO₃ (4.50 moles)was slowly added in portions to the rapidly stirred mixture, causing CO₂liberation and dissolution of the V₂ O₅ to give and essentiallyhomogeneous solution. The solution was heated at the reflux for 60minutes. The solution was then dark, blue-green due to dissolved V^(IV)which was originally present in the V₂ O₅. Approximately 1 ml of 30% H₂O₂ was added dropwise to the mixture causing the dark, black-blue greencolor to fade, leaving a slightly turbid, pale-tan sodium vanadatesolution. The solution was maintained at reflux for an additional 60minutes to ensure the decomposition of excess peroxide and then cooledto room temperature. The solution was clarified by vacuum filtration toremove the small amount (<0.2 grams) of brown solid which containedalmost all the iron and silica impurities originally present in the V₂O₅. The clear, orange sodium vanadate solution was then returned to aMorton flask, diluted with 4.0 liters distilled water, and 3886.38 gramsMoO₃ (27.00 moles) was added with rapid overhead stirring. The mixturewas heated to about 60° C. and 344.25 grams 85.4% (w/w) H₃ PO₄ (3.00moles) was added. The mixture was heated at the reflux and therebyconverted to a clear, dark, burgundy-red solution. After 3 hours atreflux, the homogenous solution was cooled to room temperature andvolumetrically diluted with distilled water to a total volume of 10.00liters, giving 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ }. The hydrogen ionconcentration of 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } was measured to be 0.35mole/liter; -log[H⁺ ]=0.45

EXAMPLE 18

Preparation of 0.30M {Na₅ HPMo₉ V₃ O₄₀ }; This solution was prepared byneutralization of 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ }with Na₂ CO₃ as follows:

15.90 grams granular Na₂ CO₃ (0.15 mole) was slowly added to 0.500 liter0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } (0.15 mole) with rapid stirring. Theresulting solution was heated to the boil for 1.5 hours (with loss ofwater volume), cooled to room temperature, and volumetrically dilutedwith distilled water to 0.500 liter. The resulting 0.30M {Na₅ HPMo₉ V₃O₄₀ } had -log [H⁺ ]=1.96.

EXAMPLES 19 and 20

Preparations of 0.30M {Na_(p) H.sub.(6-p) PMo₉ V₃ O₄₀ } solutions: Thefollowing polyoxoacid partial salt solutions designated 0.30M {Na_(P)H.sub.(6-P) PMo₉ V₃ O₄₀ } were prepared by blending 0.30M {Na₃ H₃ PMo₉V₃ O₄₀ } (Example 17) and 0.30M {Na₅ HPMo₉ V₃ O₄₀ } (Example 18) in(5-p):(P-3) volumetric ratios, and their hydrogen ion concentrationswere measured as indicated:

    ______________________________________                                        Example 19                                                                            0.30M {Na.sub.4.2 H.sub.1.8 PMo.sub.9 V.sub.3 O.sub.40 }                                          -log[H+] = 1.00                                   Example 20                                                                            0.30M {Na.sub.4.7 H.sub.1.3 PMo.sub.9 V.sub.3 O.sub.40 }                                          -log[H+] = 1.41                                   ______________________________________                                    

EXAMPLE 21

Preparation of 0.30M {Li₃ H₃ Pmo₉ V₃ O₄₀ }: The procedure was the sameas for 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } in Example 17 except that 332.51grams granular Li₂ CO₃ (4.50 moles) was substituted for the Na₂ CO₃. Thehydrogen ion concentration of the solution was measured as -log[H³⁰]=0.38

EXAMPLE 22

Preparations of 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } solutions from solid NaVO₃ ;Solutions of 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } were prepared according to thesecond reaction equation under Example 17, starting with solid sodiummetavanadate, as follows.

219.5 grams NaVO₃ (1.80 Moles) was pulverized and added to 0.40 litersdistilled water in an Erlenmayer flask and the mixture was stirred andheated until all the NaVO₃ dissolved. The solution was then cooled toroom temperature and clarified by vacuum filtration using distilledwater rinses to ensure quantitative recovery of the dissolved sodiumvanadate in the filtrate. The pale green-yellow solution was transferredto a Morton flask with distilled water added to a total volume of about2.0 liters. 777.38 grams MoO₃ (5.40 moles) was added with rapid overheadstirring. The mixture was heated to about 60° C. and 68.855 grams 84.5%(w/w) H₃ PO₄ (0.60 moles) was added. The mixture was heated at thereflux and thereby converted to a clear, dark, burgundy-red solution.After about 3 hours at reflux, the homogenous solution was cooled toroom temperature and its volume was volumetrically adjusted to 2.00liters, giving 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ }.

Four 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } solutions were prepared in this mannerfrom three different commercial sources of NaVO₃ and two differentcommercial sources of MoO₃, one of which was the same as used in Example17. (The source of H₃ PO₄ was the same in all these Examples.)

EXAMPLE 23

Measurements of chloride ion concentrations in polyoxoanion solutionsprepared from different source material; Chloride ion concentrationanalyses were made on each of six 0.30m {Na₃ H₃ PMo₉ V₃ O₄₀ } solutionsprepared from a matrix of commercial starting materials. Four of thesolutions were the ones prepared in Example 22 from three commercialNaVO₃ sources and two commercial MoO₃ sources. The other two solutionswere prepared from the same two commercial MoO₃ sources and commercialV₂ O₅ (via NaVO₃ (aq) solution) in the manner of Example 17.

Chloride ion concentrations were analyzed by AgCl-precipitatingpotentiometric titration with 1.00 mN AgNO₃ using a commercial chlorideion specific electrode (Orion) and a commercial titroprocessor (Brinkman686). The analyses were calibrated by titration of precisely weighed 1.5to 3.0 gram samples of 51.0 ppm (2.01 mM) and 102.0 ppm (4.03 mM)aqueous chloride standards, diluted to about 40 ml with distilled waterprior to titration. The accurate detection threshold was estimated to beabout 0.1 mM chloride. Precisely weighed samples of six 0.30M {Na₃ H₃PMo₉ V₃ O₄₀ } solutions, about 2.0 grams each (density=1.40 g/ml) werediluted to about 40 ml with distilled water and titrated.

The two solutions prepared from V₂ O₅ showed no detectable chloride whentitrated in this manner. They also showed no detectable chloride whenundiluted 30 grams samples were titrated. This indicates that the V₂ O₅source and the two commercial MoO₃ sources introduced no more thaninsignificant amounts of chloride into these polyoxoanion solutions.(Solutions labeled "chloride-free" throughout the Examples herein wereprepared from these starting materials.) Solutions prepared from the twocommercial MoO₃ sources and the same commercial NaVO₃ source analyzedfor essentially the same concentration of chloride, again indicatingthat the two MoO₃ sources did not introduce significant concentrationsof chloride.

Solutions prepared from the three commercial NaVO₃ sources analyzed for3.0, 8.8, and 3.7 millimolar concentrations of chloride. NaVO₃ istypically produced by dissolving V₂ O₅ in water with sodium hydroxide,bicarbonate, or carbonate in water, and evaporating the water. Wespeculate that chlorinated municipal water was used in the production ofthese NaVO₃ sources, and that chloride was concentrated into the NaVO₃product when the water was evaporated.

This example demonstrates that chloride ions in the inventive solutionsand related processes may be provided as an impurity in a startingmaterial used to prepare the polyoxoanion oxidant.

Ethylene reactions:

Examples 24 through 61 show catalyst solutions and olefin-catalystsolution mixtures within the scope of the invention and their use inprocesses for oxidation of an olefin to a carbonyl product within thescope of this invention, specifically exemplifying processes foroxidation of ethylene to acetaldehyde. In each of these examples, apalladium catalyst solution was prepared by the addition of theindicated palladium salt, as well as any other indicated solutioncomponents, to the indicated polyoxoanion oxidant solution. The hydrogenion concentration of each of the exemplified catalyst solutions was thesame as that of its parent polyoxoanion solution, as recited among thepreceding Examples.

The illustrated ethylene reactions were conducted in similarly equippedstirred tank autoclave reactors having 300 ml internal volume andfabricated of 316 stainless steel (Reactor #1), Hastelloy C (Reactor 1902), or titanium (Reactor #3). Each autoclave was equipped with a hollowshaft stirring impeller fitted with a six bladed flat disk turbine,coaxial with the cylindrical internal autoclave volume. The hollow shafthad a hole high in internal volume for gas inlet and another at theimpeller turbine for efficient dispersion of the gas phase through theliquid phase. The stirring impeller was magnetically coupled to magnetsbelted to a rheostated direct current electric motor. Each autoclave wasfitted with a vertical baffle which extended along the internal wallthrough the unstirred gas-liquid interface. Resistive electric heatingelements were jacketed to each autoclave body and were controlled by aproportioning controller which monitored the liquid solution temperaturevia a thermocouple. Volumetrically calibrated reservoirs for gasdelivery were connected to each autoclave via feed-forward pressureregulators.

The ethylene reactions were conducted in fed-batch mode, with a batch ofcatalyst solution and a continuous regulated feed of ethylene fromhigher pressure in the reservoir into the autoclave to maintain the setautoclave pressure. Thermocouples and pressure transducers monitored thetemperatures and pressures of the reaction mixture in the autoclave andthe ethylene in the reservoir, and a magnetic-sensing tachometermonitored the impeller revolution rate. These transducers were allinterfaced to a computer system for continuous data acquisition as afunction of time. Reservoir volume, pressure, and temperature data wereconverted to moles of ethylene in the reservoir using a non-ideal gasequation incorporating the compressibility of ethylene.

For each exemplified ethylene reaction, 100 milliliters of the indicatedcatalyst solution was charged to the autoclave and the gas phase in theautoclave was changed to 1 atmosphere dinitrogen. The sealed autoclavewas heated to bring the stirring solution to the indicated reactiontemperature and the autogenic pressure at this temperature was noted.With very gentle stirring of the solution, ethylene was regulated intothe autoclave to give a total autoclave pressure equal to the autogenicpressure plus the indicated ethylene partial pressure. (With only verygentle stirring of the liquid phase, gas-liquid mixing is almost nil andthe ethylene reaction is so severely diffusion limited that nodetectable reaction occurs. Gentle stirring, rather than no stirring,was provided to avoid thermal gradients in the solution.) With theautoclave open to the forward regulated total pressure from thereservoir, the reaction was initiated by increasing the impellerstirring rate to provide efficient dispersion of the gas through theliquid phase. The increase in stirring rate occurred virtuallyinstantaneously relative to the time scale of the ensuing reaction. Thereaction proceeded under constant pressure while reservoir temperatureand pressure data was collected. The decrease in moles of ethylene inthe reservoir was taken to correspond to the moles of ethylene reacted.

For every exemplified ethylene reaction for which the acetaldehydeproduct in the solution was quantitatively analyzed (by standardgas-liquid phase chromatography procedures), the reaction selectivity toacetaldehyde was ≧90%, typically ≧95%, and often ≧98%. Major by-productswere acetic acid and crotonaldehyde, which are secondary products ofacetaldehyde, by oxidation and condensation, respectively. The amountsof these by-products increased and the amount of acetaldehyde decreasedwith the amount of time the acetaldehyde-containing catalyst solutionspent at reaction temperature and subsequently at room temperature afterthe reaction of ethylene to acetaldehyde reached completion.

Statistically significant modest differences in ethylene reaction rateswere measured among the three different reactors for otherwise nominallyequivalent reactions. There differences were never more than 25%,usually less, and are attributed to differences in the accuracies of thetemperature and ethylene pressure controls among the reactors. Allrecited comparisons of results among the following Examples are drawnfrom reactions conducted in the same reactor.

Volumetric ethylene reaction rate is reported as (millimole ethyleneliter solution)/second, abbreviated mmol l⁻¹ s⁻¹. Palladium turnoverfrequency, TF, is reported as (moles ethylene/mole palladium)/second,abbreviated s⁻¹, which is the volumetric ethylene reaction rate dividedby the palladium concentration. Ethylene conversion expressed as %theory refers to the % utilization of the vanadium (V) capacity of thesolution according to reaction (12); it is 100(moles ethylenereacted)/(moles vanadium(V)/2). The palladium turnover number, TON, is(total moles ethylene reacted/moles palladium).

All the ethylene reaction described in the following Examples wereconducted under gas-liquid mixing conditions sufficient for the ethylenereaction rate to not be limited by ethylene dissolution (mass transfer)into the palladium catalyst solution. The reaction rates insteadmanifested chemical kinetics which were dependent on the palladium (ll)catalyst activity and proportional to its concentration.

EXAMPLES 24-42

Oxidation of ethylene with 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } having variouschloride concentrations; In each of these examples, a palladium catalystsolution was prepared by dissolving a palladium salt in 0.30M {Li₃ H₃PMo₉ V₃ O₄₀ } and, in some examples, also adding LiCl or HCl, asindicated in Table 2. 100 milliliters of each catalyst solution wasreacted at 120° C. with ethylene at 150 psi partial pressure in Reactor#2 using an impeller stirring rate of about 2000 RPM, usually untilethylene comsumption ceased. Table 2 lists the palladium salt and itsmillimolar concentration, the added chloride source and its millimolarconcentration, the total chloride concentration in the solution, theinitial ethylene reaction rate and palladium turnover frequency, and theethylene consumption in millimoles and as a percent of the theoreticalvanadium (V) oxidizing equivalents in the solution.

                                      TABLE 2                                     __________________________________________________________________________       palladium(II)                                                                           added    total                                                                              rate    C.sub.2 H.sub.4                            Ex.                                                                              salt      chloride chloride                                                                           mmol                                                                              Pd TF                                                                             reacted                                    No.                                                                              source mM source                                                                            mM   mM   l · s                                                                    s.sup.-1                                                                          mmol                                                                              % theory                               __________________________________________________________________________    24 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             none     0    11.8                                                                              118 45.6                                                                              101                                    25 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             none     0    11.9                                                                              119 46.1                                                                              102                                    26 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             none     0    11.4                                                                              114 45.0                                                                              100                                    27 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             none     0    11.3                                                                              113 44.9                                                                              100                                    28 PdCl.sub.2                                                                           0.10                                                                             none     0.20 12.3                                                                              123 44.0                                                                              98                                     29 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              0.20 0.20 11.5                                                                              115 43.7                                                                              97                                     30 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              1.00 1.00 12.4                                                                              124 41.9                                                                              93                                     31 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              5.00 5.00 9.7 97  43.0                                                                              96                                     32 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             HCl 5.40 5.40 9.5 95  46.0                                                                              102                                    33 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              10.2 10.2 7.4 73  39.8                                                                              89                                     34 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              15.3 15.3 5.8 57  44.5                                                                              99                                     35 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              20.1 20.1 5.2 52  48.6                                                                              108                                    36 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              26.2 26.2 4.3 43  42.5                                                                              95                                     37 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              120  120  0.77                                                                              7.7 60.2                                                                              134                                    38 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              125  125  0.82                                                                              8.2 61.26                                                                             146                                    39 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              155  155  0.62                                                                              6.2 not available                              40 PdCl.sub.2                                                                           1.00                                                                             LiCl                                                                              300  302  2.08                                                                              2.08                                                                              66.0                                                                              147                                    41 Pd(CH.sub.3 CO.sub.2).sub.2                                                          0.10                                                                             LiCl                                                                              600  600  0.07                                                                              0.67                                                                              82.7                                                                              184                                    42 PdCl.sub.2                                                                           10.0                                                                             LiCl                                                                              2000 2020 0.55                                                                              0.055                                                                             60.7                                                                              135                                    __________________________________________________________________________

EXAMPLE 43

Oxidation of ethylene with 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } having 0.010 mMpalladium(II) and 5.0 mM chloride: The procedure was the same as Example31 with the exception that the palladium(II) catalyst concentration was0.10 millimolar (1/10 the concentration of Example 31). The initialethylene reaction rate was 0.96 mmol l⁻¹ s⁻¹, corresponding to apalladium turnover frequency of 96 s⁻¹.

Comparison to Example 31 (Table 2) confirms that the ethylene reactionrate is first-order dependent on (proportional to) the palladium(II)catalyst concentration; the palladium turnover frequency is the same. Italso demonstrates that the fastest reaction rates of Table 2 and FIG. 2are not limited by by the rate of ethylene dissolution (mass transfer)into the catalyst solution, but instead manifest the chemical kineticsof the catalytic reaction.

FIG. 1 is an overlay plot of the ethylene consumption vs. time profilesfor Examples 25, 32, and 34. The slope of such a profile is the reactionrate. Since the initial reaction rate is proportional to the initialpalladium(II) catalyst concentration, the initial reaction rate (theinitial slope) indicates the activity of the initial palladium(II)catalyst. Later reaction rates, relative to the initial reaction rate,indicate the extent to which the initial palladium(II) catalyst activityis preserved through the reaction.

FIG. 1 shows that the reaction rate of Example 25, using chloride-freesolution, decelerates from its initial rate beyond about 50% conversionof the vanadium(V) to vanadium(IV). (That is, beyond about 22.5millimoles of ethylene consumed; see reaction (12)). This rate decayindicates a decreasing activity of the initial palladium(II) catalystcharge. However, at least some catalyst activity persisted to completethe conversion of the vanadium(V) to vanadium(IV) (˜45 millimoles ofethylene consumed).

The ethylene consumption vs. time profiles for the replicatechloride-free reactions of Examples 24, 25, 26, and 27, using 0.10 mMPd(CH₃ CO₂)₂ precatalyst, all exhibited essentially the same rate decayprofile. Example 28, using 0.10 mM PdCl₂ precatalyst, and Example 29,using 0.10 mM Pd(CH₃ CO₂)₂ precatalyst with 0.20 mM LiCl, exhibitedsimilar ethylene consumption vs. time profiles showing, at best, justslightly improved palladium(II) catalyst stability in this test. Theirrates still showed substantial deceleration beyond about 50% conversionof the vanadium(V). These examples demonstrate that the chlorideconcentration provided by PdCl₂ as precatalyst at 0.10 mM concentrationis not sufficient to provide substantial stabilization of the initialpalladium(II) catalyst activity to high conversion of the vanadium(V)oxidant in this test.

In contrast, the ethylene consumption vs. time profiles shown in FIG. 1for Example 32, with 5.4 mM HCl added, and Example 34, with 15.3 mM LiCladded, both using Pd(CH₃ CO₂)₂ precatalyst, are essentially linear,showing no significant rate deceleration to greater than 90% conversionof the vanadium(V) to vanadium(IV) (to at least 40 millimoles ofethylene consumed). The figure thus shows that substantial stabilizationof the initial palladium(II) catalyst activity can be obtained in theinstant invention by adding millimolar and centimolar concentrations ofchloride ions.

Examples 31 using LiCl to provide about the same chloride ionconcentration as provided by HCl in Example 32 exhibited essentially thesame ethylene consumption vs. time profile as shown for Example 27 inFIG. 1. Example 32 demonstrates that, contrary to the teaching of theMatveev patents, a hydrohalic acid, specifically HCl, may bebeneficially used in the inventive catalyst solution.

All of the Examples in Table 2 having at least millimolar concentrationsof chloride ions showed improved stabilization of the initialpalladium(II) catalyst activity to high conversion of vanadium(V)compared to the Examples which were free of chloride. All Exampleshaving at least 5 millimolar chloride ion concentration showed nosignificant rate deceleration until at least 90% conversion of thetheoretical vanadium(V) oxidizing equivalents initially present in thesolution.

Improved preservation of palladium catalyst activity in catalystsolutions and processes comprising chloride ions is also manifested inprocesses which repeatedly cycle the catalyst solution between ethylenereactions and dioxygen reactions (two-stage mode). Under conditions inwhich the ethylene reaction rate of chloride-free solutions decays fromcycle to cycle until only a substantially depressed rate is sustained,or the reaction even effectively ceases, the ethylene reaction rate ofsolutions comprising centimolar chloride ions is sustained from cycle tocycle.

FIG. 2 plots, on logarithmic axes, the initial palladium turnoverfrequency vs. chloride concentration for the Examples in Table 2. Thepalladium(II) catalyst activity is seen to be increasingly inhibited byincreasingly higher chloride ion concentrations above millimolar levels.

However, little inhibition of the palladium(II) catalyst activity isseen at millimolar chloride concentrations and only modest inhibition isseen at centimolar chloride concentrations. Such inhibition can bereadily compensated by adjusting the palladium(II) catalystconcentration to achieve the desired volumetric reaction rate. As seenin FIG. 1, although catalyst solutions with millimolar to centimolarchloride concentrations may provide initially slower reaction ratescompared to catalyst solutions free of chloride, their enhancedmaintenance of the initial rate may none-the-less provide for fastercompletion of the conversion of the vanadium(V) oxidizing equivalents.

At the highest chloride ion concentrations in FIG. 2, the log (palladiumturnover frequency) vs. log (chloride ion concentration) slope reachesthe limiting value of -2. That is, the palladium(II) catalyst activitybecomes inversely dependent on the square of the chloride ionconcentration. (The smooth dependence of turnover frequency on chlorideion concentration over Examples 40, 41, and 42, having palladium(II)concentrations of 1.00 mM, 0.10 mM, and 10,0 mM respectively, confirmsthat these rates are proportional to palladium(II) concentration and,therefore, reflect palladium(II) catalyst activity.) This limiting highchloride concentration dependence is the same chloride concentrationdependence exhibited by the Wacker system, eq (6), which uses asimilarly high chloride concentration supplied by copper chlorides. Inaqueous solutions having such high chloride ion concentrations,palladium(II) exists as the tetrachloropalladate, PdCl₄ =, which mustdissociate two chlorides to productively bind and react olefin.

The rate law for ethylene oxidation over the full range of chlorideconcentrations in FIG. 2 conforms to the following form: ##EQU1## Theconcentrations of the various palladium(II) species will be governed bythe chloride ion concentration and the equilibrium constants, under thereaction conditions, for the equilibria between these palladium species,shown in equation (18). The rate constants correspond to the catalyticactivities (turnover frequencies) of the various palladium(II) speciesunder the reaction conditions. With low or zero chloride ionconcentration, tetraaquopalladate, Pd(H₂ O)₄ ²⁺, is essentially the onlyspecies present. It is the most active palladium(II) catalyst and givesthe highest palladium turnover frequencies seen in FIG. 2. At highchloride concentrations, tetrachloropalladate, PdCl₄ =, is the dominantspecies present. It is not only much less active (k₄ <<k₀) but isseverely inhibited by the high chloride ion concentrations required forits formation.

The present invention does not require the high chloride concentrationswhich the Wacker system requires for the effective functioning of itscopper chloride co-catalyst system. Thereby, it can provide stablepalladium catalyst activities (turnover frequencies) which are one ormore orders of magnitude greater than that of the Wacker system by usingchloride ion concentrations which are one or more orders of magnitudeless than those of the Wacker system.

Also noteworthy in Table 2 is the consumption of ethylene in excess ofthe vanadium(V) oxidizing capacity of solutions having chloride ionconcentrations greater than 100 millimolar. This indicates that at thesechloride concentrations the palladium catalyst is competent to catalyzereduction of a fraction of the molybdenum(VI) in thephosphomolybdovanadate polyoxoanions to molybdenum(V). Accordingly, weanticipate that the addition of chloride ions will be useful inpalladium catalyst solutions and processes using polyoxoanions free ofvanadium (for example, PMo₁₂ O₄₀ ³⁻ and PW₆ Mo₆ O₄₀ ³⁻).

EXAMPLES 44-61

Oxidation of ethylene with 0.30M {Na_(p) H(_(5-p))PMo₁₀ V₂ O₄₀ }solutions having various hydrogen ion and chloride ion concentrations:In each of these examples, a palladium catalyst solution was prepared bydissolving Pd(CH₃ CO₂)₂ to 0.10 mM concentration in 0.30M {Na_(p)H(_(5-p))PMo₁₀ V₂ O₄₀ } (from Examples 10, 12, 13, 14, 15, and 16) and,in some examples, also adding NaCl, as indicated in Table 3. 100milliliters of each catalyst solution was reacted at 120° C. withethylene at 150 psi partial pressure in Reactor #3 using an impellerstirring rate of about 2000 RPM, usually until ethylene consumptionceased. In some of these examples, the reaction was repeated with 100milliliters virgin catalyst solution using an impeller stirring rate ofabout 3000 RPM.

Table 3 lists the sodium countercation balance, p, and hydrogen ionconcentration, -log[H⁺ ], of the phosphomolybdovanadate solution, themillimolar NaCl concentration, the initial ethylene reaction rate andpalladium turnover frequency, and the ethylene consumption. FIG. 3 plotsthe initial ethylene reaction rates and palladium turnover frequenciesof these Examples vs. the -log[H⁺ ] of their catalyst solutions.

                                      TABLE 3                                     __________________________________________________________________________                           rate                                                   Ex.                                                                              {Na.sub.p H.sub.(5-p) PMo.sub.10 V.sub.2 O.sub.40 }                                       [NaCl]  mmol                                                                              Pd TF                                                                             C.sub.2 H.sub.4 reacted                        No.                                                                              p     -log[H+]                                                                            mM  RPM l · s                                                                    s.sup.-1                                                                          mmoles                                                                             % theory                                  __________________________________________________________________________    44 2     0.18  0   2050                                                                              10.4                                                                              104 32.9 110%                                                         3010                                                                              9.7 97  31.8 106%                                      45 4     0.69  0   2060                                                                              9.2 92  28.7 96%                                                          2980                                                                              9.6 96  28.9 96%                                       46 4.40  0.91  0   2030                                                                              8.6 86  28.0 93%                                                          3020                                                                              9.1 9 1 27.3 91%                                       47 4.47  1.00  0   2050                                                                              8.2 82  25.1 84%                                       48 4.80  1.43  0   2050                                                                              4.8 48  25.0 83%                                       49 4.94  1.96  0   2050                                                                              0.7 7   23.0 77%                                       50 2     0.18  5.0 2060                                                                              10.2                                                                              102 35.2 117%                                      51 4     0.69  5.0 2080                                                                              10.3                                                                              103 29.1 97%                                       52 4.40  0.91  5.0 2040                                                                              9.3 93  25.5 85%                                       53 4.47  1.00  5.0 2050                                                                              8.5 85  25.6 85%                                       54 4.80  1.43  5.0 2060                                                                              6.4 64  23.6 79%                                       55 4.94  1.96  5.0 2050                                                                              2.0 20  21.2 71%                                       56 2     0.18  25.0                                                                              2070                                                                              4.2 42  38.2 127%                                      57 4     0.69  25.0                                                                              2070                                                                              4.3 43  30.5 102%                                      58 4.40  0.91  25.0                                                                              2040                                                                              4.8 48  28.7 96%                                       59 4.47  1.00  25.0                                                                              2030                                                                              4.8 48  28.1 94%                                       60 4.80  1.43  25.0                                                                              2040                                                                              4.2 42  24.1 81%                                       61 4.94  1.96  25.0                                                                              2060                                                                              3.4 34  23.9 75%                                       __________________________________________________________________________

Each of Examples 44, 45, and 46 show ethylene reaction rates that arenot significantly different between otherwise identical reactions usingimpeller stirring rates of about 2000 RPM and about 3000 RPM. Thisconfirms that the fastest reaction rates in Table 3 and FIG. 3 are notlimited by dissolution (mass transfer) of ethylene into the catalystsolution, but represent the chemical kinetics of catalysis under thesereaction conditions.

Examples 44-49 show that in chloride-free catalyst solutions, thepalladium catalyst activity is maximal at hydrogen ion concentrationsgreater than 0.10 moles/liter (-log[H⁺ ]<1.0) and decreasesprecipitously as the hydrogen ion concentration is decreased below 0.10moles/liter (-log[H⁺ ]<1.0). This is plausibly attributed to thedissociation of protons from the most active palladium(II) catalyst,tetraaquopalladate, Pd(H₂ O)₄ ²⁺ (reportedly having two aciddissociation constants with pK_(a) ˜2) to give relatively inactivehydroxo-aquo palladium (II) species.

The Examples in Table 3 (FIG. 3) having -log[H⁺ ]<1.0 again show thatpalladium catalyst activity is not significantly inhibited by chlorideions at 5 mM concentration, and is 40-60% inhibited by chloride ions at25 mM concentration. (These are essentially the same responses as with0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } seen in the Examples of Table 2 (FIG. 2).)Analogous to FIG. 1, the ethylene consumption vs. time profiles of thesereactions using solutions with 5.0 mM and 25 mM chloride concentrationsmanifested substantial stabilization of the initial palladium(II)catalyst activity through the reaction as compared to the correspondingreactions of chloride-free solutions.

The Examples in Table 3 also show that, in contrast to the inhibition by25 mM chloride in solutions having -log[H⁺ ]<1.0, palladium catalystactivity in solutions having -log[H⁺ ]˜2.0 is surprisingly promoted bythe addition of chloride ions up to at least 25 mM concentration. FIG. 3shows that while chloride-free solutions give precipitously decreasingpalladium activity as the hydrogen ion concentration is decreased below0.10M to about 0.01M (-log[H⁺ ]>1.0 to about 2.0), solutions with 5 mMchloride give less severely decreasing palladium activity and solutionswith 25 mM chloride give little significant decrease in palladiumactivity.

This promotion of palladium catalyst activity by chloride at -log[H⁺ ]>1is plausibly attributed to the formation of chloro-aquo palladium(II)species (equation (18)) which have higher pK_(a) 's thantetraaquopalladate, reflecting their lower positive charge. Accordingly,these chloro-aquo palladium(II) species do not dissociate protons togive catalytically less active hydroxo-species until higher -log[H⁺ ]than does tetraaquopalladate. As the chloride ion concentration isfurther increased above 25 mM, the palladium(II) will eventually becomePdCl₃ - and PdCl₄ =and its catalytic activity will then again beinhibited by increasing chloride concentration, as indicated in theabove rate equation.

Accordingly, the palladium(II) catalyst activity dependence on chlorideion concentration at a -log[H⁺ ]>1.0 has a maximum at chloride ionconcentrations greater than zero (in contrast to the chloride ionconcentration dependence shown in FIG. 2 for -log[H⁺ ]<1.0). The maximumpalladium(II) catalyst activity will be at increasingly higher chlorideion concentration as the hydrogen ion concentration of the solution isfurther diminished below 0.10 mole/liter (-log[H⁺ ] increasingly greaterthan 1.0). For example, FIG. 2 shows that 5 mM chloride provides greateractivity than 25 mM chloride at -log[H⁺ ]≅1.4, and that 25 mM chlorideprovides greater activity than 5 mM chloride at -log[H⁺ ]≅2.0. Thechloride ion concentration which provides maximal palladium(II) catalystactivity at any set hydrogen ion concentration, as well as the hydrogenion concentration which provides maximal palladium(II) catalyst activityat any set chloride ion concentration, can be readily determined byroutine experimentation, using, for example, the techniques exemplifiedherein.

The Examples in Table 3 also show that as the hydrogen ionconcentrations is decreased (-log[H⁺ ] is increased), particularly athydrogen ion concentrations less than 0.10 (-log[H⁺ ]>1), the ethylenereacted appears reduced below the theoretical capacity of the initialvanadium(V) concentration, whether the solution is chloride-free orcontains up to 25 mM chloride. (See likewise Examples 62-65 and FIG. 4.)While the solutions containing 25 mM chloride all showed comparableinitial reaction rates, only the solutions with -log[H⁺ ]<1.0 gavesufficient preservation of the initial rate to complete conversion ofthe vanadium(V) (to 30 millimoles ethylene consumed.)

Accordingly, in some embodiments of the present invention, the hydrogenion concentration is preferably at least 0.10 moles/liter (-log[H⁺ ]<1),even though the chloride ion concentration may be sufficient to providea comparable initial palladium catalyst activity at hydrogen ionconcentrations less than 0.10 moles/liter. The palladium(II) catalystactivity is most stable when the aqueous solution comprises bothchloride ions and a concentration of hydrogen ions greater than 0.10moles/liter. Usually, the greater the concentration of hydrogen ions(the more acidic the solution), the lesser is the concentration ofchloride ions required to provide the desired stability of palladiumcatalyst activity.

EXAMPLES 62-65

Oxidation of ethylene with 0.30M {Na_(p) H.sub.(6-p) PMo₉ V₃ O₄₀ }solutions having various hydrogen ion and containing 25 mM chloride: Ineach of these examples, a palladium catalyst solution was preparedcontaining 0.10 mM Na₂ PdCl₄ and 24.6 mM NaCl in 0.30M {Na_(p)H.sub.(6-p) PMo₉ V₃ O₄₀ } (from Examples 17, 18, 19, and 20). 100milliliters of each catalyst solution was reacted at 120° C. withethylene at 150 psi partial pressure in Reactor #3 using an impellerstirring rate of about 2000 RPM until ethylene consumption ceased. Table4 lists the sodium countercation balance, p, and hydrogen ionconcentration, -log[H⁺ ], of the phosphomolybdovanadate solution, theinitial ethylene reaction rate and palladium turnover frequency, and theethylene consumption.

                                      TABLE 4                                     __________________________________________________________________________                     rate                                                              {Na.sub.p H.sub.(6-p) PMo.sub.9 V.sub.3 O.sub.40 }                                        mmol                                                                              Pd TF                                                                             C.sub.2 H.sub.4 reacted                              Example                                                                            p     -log[H+]                                                                            l · s                                                                    s.sup.-1                                                                          mmoles                                                                             % theory                                        __________________________________________________________________________    62   3     0.45  3.3 33  43.7 97                                              63   4.2   1.00  3.7 37  44.1 98                                              64   4.7   1.41  3.4 34  38.8 86                                              65   5     1.96  2.3 23  35.6 79                                              __________________________________________________________________________

Table 4 shows again that centimolar chloride ion concentrations canprovide initial palladium(II) catalyst activities in solutions with-log[H⁺ ]`1 comparable to those obtained in solutions with -log[H⁺ ]<1.It also shows again that as -log[H⁺ ] is increased >1, the ethyleneconsumption appears reduced below the theoretical capacity of theinitial vanadium(V) concentration, even in solutions containing 25 mMchloride.

FIG. 4 is an is an overlay plot of the ethylene consumption vs. timeprofiles for Examples 62, 64, and 65. (Example 63's profile issubstantially the same as Example 62's and is omitted from the Figurefor clarity). The figure shows that as the -log[H⁺ ] is increased >1,the initial reaction rate increasingly decelerates over the course ofthe reactions, indicating increased deactivation of initialpalladium(II) catalyst activity. This results ultimately in ceasedethylene consumption short of theory on the initial vanadium(V) oxidantcapacity in the reactions with -log[H⁺ ]>1. While the solutions inExamples 62-65 all showed comparable initial reaction rates, only thesolutions with -log[H⁺ ]<1.0 gave sufficient preservation of the initialrate to complete conversion of the vanadium(V) (to about 45 millimolesethylene consumed.)

More rigorous and discriminating tests of catalyst stability (forexample. multipass ethylene-dioxygen reactions) reveal that even amongsolutions with -log[H⁺ ]<1.0, palladium(II) catalyst stability isfavored by greater hydrogen ion concentrations. That is, 0.30M {Na₃ H₃PMo₉ V₃ O₄₀ } provides for increased preservation of initialpalladium(II) activity compared to 0.30M {Na₄.2 H₁.8 PMo₉ V₃ O₄₀ }(which was not markedly revealed in the test of Examples 62-65), and0.30M {Na_(p) H.sub.(5-p) PMo₁₀ V₂ O₄₀ } with p<3 would provide stillfurther increased catalyst stability. Viewed another way, the greaterthe concentration of hydrogen ions (the more acidic the solution), thelesser is the concentration of chloride ions required to provide thesame degree of palladium (II) catalyst stability.

EXAMPLE 66

Oxidation of ethylene with chloride-free 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ }: Apalladium catalyst solution was prepared containing 0.076 mM Pd(CH₃CO₂)₂ in chloride-free 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } prepared from V₂ O₅as in Example 17. 100 milliliters of the solution was reacted at 120° C.with ethylene at 150 psi partial pressure in Reactor #2 using animpeller stirring rate of about 2000 RPM. The initial volumetricethylene reaction rate was 7.6 mmol l⁻¹ s⁻¹, corresponding to apalladium turnover frequency of 100 s⁻¹. Beyond about 10 millimoles ofethylene reacted (˜25% conversion of the initial vanadium(V) oxidizingequivalents) the reaction rate increasingly decelerated and the reactionrequired about 240 seconds complete its consumption of ethylene at 41.8millimoles (corresponding to 93% vanadium(V) conversion.)

EXAMPLE 67

Oxidation of ethylene with 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } solutioncontaining 3 mM chloride provided as an impurity in the startingmaterials used for its preparation: The procedure was the same as inExample 66 with the exception that the 0.30M {Na₃ H₃ PMo₉ V₃ O₄₀ } wasprepared from commercial solid NaVC₃ as in Example 22, and analyzed for3 mM chloride (Example 23). The initial volumetric ethylene reactionrate was 8.1 mmol l⁻¹ s⁻¹, corresponding to a palladium turnoverfrequency of 107 s⁻¹. The reaction rate decelerated only slightly overthe course of the reaction, which completed its consumption of ethyleneat 42.7 millimoles (95% vanadium(V) conversion) within 70 seconds.

Comparison with Example 66 demonstrates that chloride ions provided asan impurity in a starting material used to prepare the polyoxoanionoxidant are effective for providing improved stability of palladiumcatalyst activity.

Butene reaction:

The following example shows a catalyst solution within the scope of thisinvention used in a process for the oxidation of 1-butene to 2-butanonewithin the scope of this invention. The 1-butene reaction was conductedin a 300 ml Hastelloy C stirred tank autoclave reactor equippedsimilarly to the previously described reactors used for the precedingexamples of ethylene reactions. The volumetrically calibrated 1-butenereservoir and its feed lines to the reactor were heated to keep thecontained 1-butene in the gas state. The reaction was conducted infed-batch mode by the methods described for the ethylene reactions.

EXAMPLE 68

Oxidation of 1-butene with 0.30M [Li₃ H₃ PMo₉ V₃ O₄₀ }: A catalystsolution was prepared containing 0.60 mM Pd(CH₃ CO₂)₂ and 30 mM LiCldissolved in 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } (Example 21), having -log[H⁺]=0.38.

150 milliliters of this catalyst solution was reacted at 130° C. with1-butene at 200 psi partial pressure using an impeller stirring rate ofabout 2000 RPM. The initial volumetric rate of 1-butene reaction was 5.9mmol l⁻¹ s⁻¹, corresponding to a palladium turnover frequency of 10 s⁻¹.The stirring was stopped 60 seconds after its initiation to stop thereaction. 26 millimoles of 1-butene were consumed within that time,giving 2-butanone as the predominant product.

Multiple Pass Ethylene-Dioxygen reactions:

Example 69 through 72 show processes for oxidation of an olefin to acarbonyl product within the scope of this invention, specificallyexemplifying multiple-pass processes for oxidation of ethylene toacetaldehyde with intermediate reoxidation of reduced polyoxoanionsolution by reaction with dioxygen. These reactions were conducted in aglass stirred tank autoclave reactor having 750 ml internal volume,equipped with a hollow shaft stirring impeller fitted with amulti-bladed flat disk turbine, coaxial with the cylindrical internalautoclave volume. The hollow shaft had a hole high in internal volumefor gas inlet and another at the impeller turbine for efficientdispersion of the gas phase through the liquid phase. The stirringimpeller was magnetically coupled to magnets belted to a rheostateddirect current electric motor. The autoclave was fitted with a verticalbaffle which extended along the internal wall through the unstirredgas-liquid interface. The autoclave was double walled with a jacket forcirculation of heating fluid from a thermostated recirculating bath.Volumetrically calibrated reservoirs for ethylene and dioxygen deliverywere connected to the autoclave via feed-forward pressure regulators.

The ethylene reactions were conducted in fed-batch mode, with a batch ofcatalyst solution and a continuous regulated feed of ethylene fromhigher pressure in the reservoir into the autoclave to maintain the setautoclave pressure. Thermocouples and pressure transducers monitored thetemperatures and pressures of the reaction mixture in the autoclave andof the ethylene in the reservoir, and a magnetic-sensing tachometermonitored the impeller revolution rate. These transducers were allinterfaced to a computer system for continuous data acquisition as afunction of time. Reservoir volume, pressure, and temperature data wereconverted to moles of ethylene in the reservoir using a non-ideal gasequation incorporating the compressibility of ethylene.

For example, 150 milliliters of the indicated catalyst solution wascharged to the autoclave and the gas phase in the autoclave was chargedto 1 atmosphere dinitrogen. The sealed autoclave was heated to 120° C.bring the stirred solution to 120° C. and the autogenic pressure at thistemperature was noted. With very gentle stirring of the solution,ethylene was regulated into the autoclave to give a total autoclavepressure equal to the autogenic pressure plus an ethylene partialpressure of 130 psia. With the autoclave open to the forward regulatedtotal pressure from the reservoir, the reaction was initiated byincreasing the impeller stirring to the indicated rate. The ethylenereaction proceeded under constant pressure while reservoir temperatureand pressure data was collected. The decrease in moles of ethylene inthe reservoir was taken to correspond to the moles of ethylene reacted.

The first pass ethylene reaction was allowed to proceed unit 40millimoles of ethylene was consumed by reaction. At that time, theethylene reaction was essentially terminated by stopping the stirring.Subsequent passes of ethylene reactions were allowed to proceed for thesame amount of time as the first pass and their ethylene consumptionswithin that time were recorded.

Immediately following each ethylene reaction, the gas space in thereactor was flushed with nitrogen for 3-4 minutes, after which oxygenwas regulated into the autoclave to give a total autoclave pressureequal to the autogenic pressure plus a dioxygen partial pressure of 130psia. With the autoclave open to the forward regulated total pressurefrom the dioxygen reservoir, the reaction was initiated by increasingthe impeller stirring to 2000 RPM. Dioxygen reactions were allowed toproceed for 1 minute, after which the stirring was stopped and the gasspace in the reactor was again flushed with nitrogen for 3-4 minutes.The reaction solution temperature was maintained at 120° C. throughoutthis operation. Subsequent passes of ethylene reactions immediatelyfollowed.

EXAMPLE 69

Multiple-pass ethylene oxidation reactions with chloride-free 0.30M {Li₃H₃ PMo₉ V₃ O₄₀ } under chemical kinetics control: 150 milliliters of apalladium catalyst solution containing 0.15 mM Pd (CH₃ CO₂)₂ in 0.30M{Li₃ H₃ PMo₉ V₃ O₄₀ } (Example 21) was reacted with ethylene over 15passes by the procedure described above using an impeller stirring rateof 2000 RPM. This stirring rate was independently confirmed to providegas-liquid mixing sufficient to avoid any gas-liquid diffusionlimitation on the reaction rate.

In the first pass ethylene reaction, 40 millimoles ethylene was reactedin 30 seconds. Over the next seven passes, the amount of ethylenereacted in 30 seconds decreased to about 25 millimoles. Over the lasteight passes, the amount of ethylene reacted in 30 seconds remainedconstant at about 25 millimoles.

This example demonstrates that, at best, about 60% of the initialpalladium(II) catalyst activity could be sustained in this chloride-freesolution under these multipass reaction test conditions.

EXAMPLE 70

Multiple-pass ethylene oxidation reactions with 0.30M }Li₃ H₃ PMo₉ V₃O₄₀ } containing 5.0 mM chloride, under chemical kinetics control: Theprocedure was the same as for Example 69 with the exception that 5.0millimolar LiCl was added in the catalyst solution.

In the first pass ethylene reaction, 40 millimoles ethylene was reactedin 30 seconds. This is the same amount of time required to react 40millimoles ethylene in the first pass of Example 69, showing that 5.0millimolar chloride ions causes no significant inhibition ofpalladium(II) catalyst activity. In each of the following fourteenethylene reaction passes, the amount of ethylene reacted in 30 secondswas 40 millimoles or modestly greater.

Comparison with Example 69 demonstrates that the addition of chloride inthe present Example provided essentially complete preservation of theinitial palladium catalyst activity under these multipass reaction testconditions.

EXAMPLE 71

Multiple-pass ethylene oxidation reactions with chloride-free 0.30M {Li₃H₃ PMo₉ V₃ O₄₀ } under gas-liquid diffusion control: The procedure wasthe same as for Example 69 with the exception that the impeller stirringrate for the ethylene reactions was 500 RPM. (The impeller stirring ratefor the dioxygen reactions remained at 2000 RPM.) The first passethylene reaction proceeded at a slower rate than that of Example 69,confirming that the reaction rate was limited by gas-liquid diffusion atthis slower stirring rate.

In the first pass ethylene reaction, 40 millimoles ethylene was reactedin 100 seconds. In the second pass ethylene reaction, only 16 millimolesethylene was reacted in 100 seconds. By the seventh pass, the amount ofethylene reacted in 100 seconds decreased to about 12.5 millimoles, andremained constant at that amount over the remaining passes.

Comparison with Example 69 demonstrates that only half as much palladiumcatalyst activity could be sustained in this chloride-free solutionunder this multipass reaction protocol when the reaction rate waslimited by the rate of ethylene dissolution into the catalyst solution,than in the same solution when the mixing conditions were sufficient toavoid such limitation.

EXAMPLE 72

Multiple-pass ethylene oxidation reactions with 0.30M {Li₃ H₃ PMo₉ V₃O₄₀ } containing 0.5 mM chloride, under gas-liquid diffusion control:The procedure was the same as for Example 71 with the exception that 5.0millimolar LiCl was added in the catalyst solution. This procedure wasthe same as for Example 70 with the exception that the impeller stirringrate for the ethylene reactions was 500 RPM.

In the first pass ethylene reaction, 40 millimoles ethylene was reactedin 110 seconds. In each of the following fourteen ethylene reactionpasses, the amount of ethylene reacted in 110 seconds was 40 millimolesor modestly greater.

Comparison with Example 71 demonstrates that the addition of chloride ithe present Example provided for essentially complete preservation ofthe initial palladium catalyst activity under these multipass reactiontest conditions, even when the reaction rate was limited by the rate ofethylene dissolution into the catalyst solution.

In contrast to the teachings of the Matveev patent Examples, we foundthat initial catalyst activity could not be stably sustained in suchmultipass reactions using chloride-free polyoxoanion solutions. Stablecatalyst activity could be sustained at its initial level only byproviding chloride in the polyoxoanion solution. Chloride could beprovided by intentional addition of a chloride ion source to thepolyoxoanion solution or by preparing the polyoxoanion solution fromstarting materials containing chloride as an impurity (see Examples 22and 23), or both. For this purpose, the chloride ion concentration ispreferably greater than twice the palladium catalyst concentration; mostpreferably, at least 5 millimolar.

Palladium Metal Oxidative Dissolution Reactions:

Examples 73 through 76 show processes for oxidation of palladium (0) topalladium (II) within the scope of this invention and their use inprocesses for oxidation of an olefin to a carbonyl product within thescope of this invention.

In each of these examples, palladium (0) metal and 100 milliliters ofthe indicated polyoxoanion solution were charged to the autoclaveReactor #2. described above and used for preceding examples of ethylenereactions. The gas phase in the sealed autoclave was changed to eithernitrogen or dioxygen and the mixture was stirred and heated as describedin each example. Following this heat treatment, the mixture was reactedwith ethylene at constant 150 psi partial pressure (fed-batch mode)using an impeller stirring rate of about 2000 RPM. following theprocedure previously described for the preceding examples of ethylenereactions.

By dividing the measured initial reaction rate by the known palladium(II) catalyst turnover frequency (independently measured under identicalreaction conditions by using a palladium(II) salt as precatalyst) theconcentration of active palladium (II) catalyst present in the solutionafter the heat treatment could be calculated.

EXAMPLE 73

Oxidative dissolution of palladium (0) metal by chloride-free 0.30M {Li₃H₃ PMo₉ V₃ O₄₀ }; 1.1 milligram (0.010 millimole) palladium powder(1.0-1.5 micron, surface area=1.6 m² /g) and 100 milliliters a 0.30M{Li₃ H₃ PMo₉ V₃ O₄₀ } were charged to the autoclave reactor and the gasphase in the sealed autoclave was changed to 1 atmosphere dinitrogen.The stirring solution was heated to 120° C. and maintained at thattemperature for 2 hours. With very gentle stirring of the solution,ethylene was then regulated into the autoclave to 150 psi partialpressure, and the ethylene reaction was initiated by increasing theimpeller stirring rate to about 2000 RPM.

The initial ethylene reaction rate was 0.11 mmol l⁻¹ s⁻¹. The reactionwas discontinued after 45 minutes, having consumed less than 20millimoles ethylene (<50% conversion of vanadium (V) to Vanadium (IV)).

Examples 24-27 show ethylene reactions using the same 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀ } polyoxoanion solution under the same reaction conditionsprovided the same molar amount of palladium, but provided as palladium(II) acetate. The average initial reaction rate for these examples is11.6 mmol l⁻¹ s⁻¹, corresponding to a palladium turnover frequency of116 s⁻¹. As seen in FIG. 1 for Example 25, these reactions consumedethylene to the complete vanadium (V) oxidizing capacity of the solution(45 millimoles ethylene) within about 90 seconds.

Accordingly, only about 1% of the palladium (0) metal provided in thepresent example was oxidatively dissolved to active palladium(II)catalyst during the heat treatment prior to the ethylene reaction.

EXAMPLE 74

Oxidative dissolution of palladium(0) metal by chloride-free 0.30M {Li₃H₃ PMo₉ V₃ O₄₀ }: The procedure was the same as for Example 73 with theexception that the 2 hour heat treatment was at 170° C. The solution wascooled to 120° C. for the ethylene reaction. The initial ethylenereaction rate was 4.0 mmol l⁻¹ s⁻¹.

Comparison with Examples 24-27 shows that about 35% of the palladium(0)metal provided in the present example was oxidatively dissolved toactive palladium (II) catalyst during the 2 hour, 170° C. heat treatmentprior to the ethylene reaction.

EXAMPLE 75

Oxidative dissolution of palladium (0) metal by chloride-free 0.30M {Li₃H₃ PMo₉ V₃ O₄₀ } under dioxygen: The procedure was the same as forExample 73 with the exception that the two hour heat treatment at 120°C. was conducted with 100 psi partial pressure of dioxygen using animpeller stirring speed of about 2000 RPM. After this heat treatment,the mixture was cooled to ambient temperature, the gas phase inautoclave was changed to 1 atmosphere dinitrogen, and the mixture wasreheated to 120° C. for the ethylene reaction. The initial ethylenereaction rate was 0.08 mmol l⁻¹ s⁻¹. The reaction was discontinued after45 minutes, having consumed less than 12 millimoles ethylene.

Comparison with Example 73 shows that the addition of dioxygen to achloride free polyoxoanion solution does not significantly promote itskinetic capability to oxidatively dissolve palladium (0) metal to activepalladium (II) catalyst.

EXAMPLE 76

Oxidative dissolution of palladium (0) metal by 0.30M {Li₃ H₃ PMo₉ V₃O₄₀ } containing chloride ions: The procedure was the same as forExample 73 with the exceptions that LiCl was added in the polyoxoanionsolution at 15.0 mM concentration and the ethylene reaction wasinitiated after only 1 hour of heat treatment at 120° C.

The initial ethylene reaction rate was 5.8 mmol l⁻¹ s⁻¹, correspondingto a palladium turnover frequency of 58 s⁻¹. The reaction consumed 43.4millimoles ethylene (96% of theory on the vanadium (V) oxidizingcapacity) within about 75 seconds. The reaction rate and ethyleneconsumption vs. time profile were essentially the same as for Example 34(see Table 2 and FIG. 1), which used the same 0.30M {Li₃ H₃ PMo₉ V₃ O₄₀} polyoxoanion solution, containing about the same concentration ofchloride ions, under the same reaction conditions and provided the samemolar amount of palladium, but provided as palladium (II) acetate. Thiscomparison demonstrates that essentially 100% of the palladium (0) metalprovided in the present example was oxidatively dissolved to activepalladium (II) catalyst during the heat treatment prior to the ethylenereaction.

Comparison to Example 73 demonstrates that the presence of chloride ionsin the instant invention critically enables the polyoxoanion oxidant torelatively rapidly oxidize palladium (0) metal to active palladium (II)catalyst. In contrast to the teachings of the Matveev patents,specifically Matveev patents' Example 10, we found that palladium metalcould not be directly and facilely used to provide a corresponding molaramount of active palladium catalyst in chloride-free polyoxoanionsolutions. Chloride ions can be provided in the present invention byintentional addition of a chloride ion source to the polyoxoanionsolution or by preparing the polyoxoanion solution from startingmaterials containing chloride as an impurity (see Example 22), or both.

The present inventions have been shown by both description andexemplification. The exemplification is only exemplification and cannotbe construed to limit the scope of the invention. Persons of ordinaryskill in the art will envision equivalents to the inventive solutionsand processes described by the following claims which are within thescope and spirit of the claimed invention.

We claim as our invention:
 1. An aqueous palladium catalyst solution forthe oxidation of an olefin to a carbonyl product comprising a palladiumcatalyst, a polyoxoanion oxidant comprising vanadium, and chloride ions,wherein the concentration of said chloride ions is greater than twicethe concentration of said palladium catalyst and at least 5 millimoleper liter.
 2. The solution of claim 1 wherein said chloride ions areprovided as an impurity in a starting material used to prepare saidpolyoxoanion oxidant.
 3. The solution of claim 1 wherein saidpolyoxoanion oxidant further comprises phosphorus and molybdenum.
 4. Thesolution of claim 3 wherein said polyoxoanion oxidant comprises aphosphomolybdovanadate having the formula

    [H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-

wherein 0<x<12 and 0≦y<(3+x), or mixtures thereof.
 5. The solution ofclaim 1, 2, 3, or 4, wherein the concentration of hydrogen ions in theaqueous solution is greater than 0.10 mole per liter of solution whenessentially all the oxidant is in its oxidized state.
 6. The solution ofclaim 1, 2, 3, or 4, further comprising at least one of an olefin and acorresponding carbonyl product.
 7. A process for oxidation of an olefinto a carbonyl product comprising:reacting the olefin with an aqueouscatalyst solution, wherein the aqueous catalyst solution is the solutionof claim 1, 2, 3, or 4, at conditions sufficient to oxidize the olefinto a carbonyl product.
 8. A process for oxidation of an olefin to acarbonyl product comprising:reacting the olefin with an aqueous catalystsolution comprising a palladium catalyst, a polyoxoanion oxidantcomprising vanadium, and chloride ions, wherein the concentration ofsaid chloride ions is greater than twice the concentration of saidpalladium catalyst and at least 5 millimole per liter, at conditionssufficient to oxidize the olefin to a carbonyl product.
 9. The processof claim 8 wherein said chloride ions are provided as an impurity in astarting material used to prepare said polyoxoanion oxidant.
 10. Theprocess of claim 8 wherein said polyoxoanion oxidant further comprisesphosphorus and molybdenum.
 11. The process of claim 10 wherein saidpolyoxoanion oxidant comprises a phosphomolybdovanadate having theformula

    [H.sub.y PMo.sub.(12-x) V.sub.x O.sub.40 ].sup.(3+x-y)-

wherein 0<x<12 and 0≦y<(3+x), or mixtures thereof.
 12. The process ofclaim 8, 9, 10, or 11, wherein the olefin is ethylene and the carbonylproduct is acetaldehyde.
 13. The process of claim 8, 9, 10, or 11,wherein the olefin is propylene and the carbonyl product is acetone. 14.The process of claim 8, 9, 10, or 11, wherein the olefin is one of1-butene, cis-2-butene, and trans-2-butene, or mixtures thereof, and thecarbonyl product is 2-butanone.
 15. The process of claim 8, 9, 10, or11, wherein the olefin is one of 3-methyl-1-butene and2-methyl-2-butene, or mixtures thereof, and the carbonyl product is3-methyl-2-butanone.
 16. The process of claim 8, 9, 10, or 11, whereinthe olefin is 4-methyl-1-pentene and the carbonyl product is4-methyl-2-pentanone.
 17. The process of claim 8, 9, 10, or 11, whereinthe olefin is cyclopentene and the carbonyl product is cyclopentanone.18. The process of claim 8, 9, 10, or 11, wherein the olefin iscyclohexene and the carbonyl product is cyclohexanone.
 19. The processof claim 8, 9, 10, or 11, further comprising contacting dioxygen withthe aqueous catalyst solution.
 20. The process of claim 8, 9, 10, or 11,further comprising the steps of removing the carbonyl product from theaqueous solution, reacting dioxygen with the aqueous catalyst solutionat conditions sufficient to regenerate the oxidant in its oxidizedstate, and reacting additional olefin with the aqueous catalystsolution.
 21. In an aqueous palladium catalyst solution for theoxidation of an olefin to a carbonyl product comprising a palladiumcatalyst and a polyoxoanion oxidant comprising vanadium, the improvementwherein the solution further comprises chloride ions at a concentrationgreater than twice the concentration of said palladium catalyst and atleast 5 millimolar per liter.
 22. In a process for oxidation of anolefin to a carbonyl product comprising reacting the olefin with anaqueous catalyst solution comprising a palladium catalyst and apolyoxoanion oxidant comprising vanadium at conditions sufficient tooxidize the olefin to a carbonyl product, the improvement wherein thesolution further comprises chloride ions at a concentration greater thantwice the concentration of said palladium catalyst and at least 5millimolar per liter.